What’s New in Emacs 31.1?

Emacs 31.1 is finally out! Unlike earlier Emacs versions, there is not a singular big-bang feature in this release. From what I could gather, the new garbage collector was possibly planned for inclusion in Emacs 31.1, but it has been postponed to Emacs 32. But more on that in a future post; it’s an interesting subject.

Some of the more notable features in Emacs 31.1 are small, quality of life fixes, and one deprecation that marks the end of an era.

As always, my book, Mastering Emacs is 31% off for the next week to celebrate the release also.

The unexec/pdumper controversy and subsequent deprecation

Emacs is… not a normal application. When you compile and link it, you get temacs which is the heart of Emacs but without most of the libraries that ship with it. It’s a bare-bones Emacs with little more than the C core and the interpreter; it’s not really that useful.

To get the Emacs binary you know and love, you have to run temacs and tell it to load the standard library into memory. That is slow. There is a lot of elisp and housekeeping that has to happen. It can take several minutes and a fair bit of CPU and ram to start Emacs this way; it’s untenable.

This has been a problem that has dogged Emacs for decades. It’s not a huge deal today, but back in the day it could break the back on home computers or even shared multi-user environments if a brace of enthusiastic Emacs users all decide to launch Emacs at the same time in the morning.

The solution to this problem? Load it all in once and then literally dump the text/data/bss/etc. segments of Emacs’s memory to a new binary. Do that, and you don’t have to bootstrap all that Emacs lisp state again and again. It feels like a wrestling move almost. You corral a top-heavy Emacs into position and apply The Attitude Adjustment, body slamming Emacs into a new binary, and everything’s all set up and ready to go.

It’s a pretty boss move.

But to make this, uh, wrestling move work, Emacs depended on a number of snowflake functions in glibc. After a couple of decades of enabling this sort of bad behavior the glibc team called it quits, and Emacs had to find another way of doing it.

Daniel Colascione built a much better solution, though not everyone was happy about it, that – put simply – standardizes the serialization of Emacs’s internal structures into something that is not a 1:1 dump of its internal memory structures.

The portable dumper’s been the default for a number of years now. It was first introduced around ten years ago, and in keeping with Emacs’s long history of backwards compatibility, the old unexec dumper was kept around ostensibly for the one or two users who found the idea of a portable dumper risible or unworkable.

But now it is finally gone for good. The end of an era.

User Lisp Directory

Classic problem: you git clone or download an Emacs package somewhere and now you want it to work. But how? It’s not that trivial; there are quite a few competing ways of doing it. The simplest one is to tell users to drop their package into the user-lisp/ in your .emacs.d directory and Emacs will sort out loading and setting up autoload (so the right stuff appears in M-x.)

Small feature, huge benefit, with a caveat. For some reason use-package has had its :vc feature deprecated; they only just added it in 30.1. Odd.

Minibuffer and Completions

Emacs 30.1 gained completion-preview-mode, a native “pop-up window” system not unlike Company and Corfu, but more attuned to Emacs’s own way of doing things: using the *Completions* window instead of a floating child frame like Company and friends.

Emacs 31.1 builds on that with a wide range of customizable options you’re sure to want to customize if you want to go native.

Rotating Window Layouts

M-x window-layout-rotate-clockwise (see C-x w C-h for the manifold new options) and suchlike rotate your window layouts. Another little UI winner.

Exchanging the point and mark without activating the region

I’ve talked (mostly in the my book) about how transient-mark-mode is a rather awkward one-size-fits-all that was draped over Emacs’s multitude of “region-affecting” commands, like kill-region (C-w).

So C-x C-x, that exchanges point and mark, also activates the region whether you want it to or not. Fixing the mark commands in transient mark mode is an old article of mine where I demonstrate how to do exactly that. But now there’s a builtin option to not have it do that — sweet.

Tree-sitter now offers to install its grammars for you

Two blockers work in tandem to hold back the wider adoption of tree-sitter in Emacs:

1. The fact that TS demands a special major mode to work; and that said mode is often a thread-bare re-implementation of the original.
2. That installing grammars, especially on Windows, is a giant pain in the neck, as you have to not only thread the needle with the exacting ABI version of the tree-sitter library itself, but also ensure you just the exacting version of each language grammar, or everything goes up in smoke.

The former is still a problem, but the latter is now mostly resolved. Emacs can now finally offer to install the right language grammar for TS modes it knows about.

Now there’s no excuse not to try out Combobulate: Structured Movement and Editing with Tree-Sitter.

and so much more

Lots of little tweaks and changes. Have a read.

Installation Changes in Emacs 31.1

unexec dumper removed.
The traditional unexec dumper, deprecated since Emacs 27, has been
removed.

The portable dumper now works on m68k a.out targets.

As I wrote in the introduction at the top, this is indeed the end of an era.

Emacs's old 'ctags' program is no longer built or installed.
You are encouraged to use Universal Ctags <https://ctags.io/> instead.
For now, to get the old 'ctags' behavior you can can run 'etags --ctags'
or use a shell script named 'ctags' that runs 'etags --ctags "$@"'.

If you’re a TAGS user you should check with where and make sure you’ve got a newer one installed. (If you don’t know if you use TAGS, you do not.)

Changed GCC default options on 32-bit x86 systems.
When using GCC 4 or later to build Emacs on 32-bit x86 systems,
'configure' now defaults to using the GCC options '-mfpmath=sse' (if the
host system supports SSE2) or '-fno-tree-sra' (if not).  These GCC
options work around GCC bug 58416, which can cause Emacs to behave
incorrectly in rare cases.

New configure option '--with-systemduserunitdir'.
This allows specifying the directory where the user unit file for
systemd is installed; the default is '${prefix}/usr/lib/systemd/user'.

You can tell Emacs to install a systemd service to run Emacs’s server that way. I recommend doing this.

Startup Changes in Emacs 31.1

In compatible terminals, 'xterm-mouse-mode' is turned on by default.
For these terminals the mouse will work by default.  A compatible
terminal is one that supports Emacs setting and getting the OS selection
data (a.k.a. the clipboard) and mouse button and motion events.  With
'xterm-mouse-mode' enabled, you must use Emacs keybindings to copy to the
OS selection instead of terminal-specific keybindings.

You can keep the old behavior by customizing 'xterm-mouse-mode' to nil.

Most people do not know this but Emacs added mouse support to terminal Emacs years ago but left it off. Terminal capabilities vary widely so that was a nice and safe decision. But now it just works as you’d expect it to: menus are clickable and so forth. Good stuff.

site-start.el is now loaded before the user's early init file.
Previously, the order was early-init.el, site-start.el and then the
user's regular init file, but now site-start.el comes first.  This
allows site administrators to customize things that can normally only be
done from early-init.el, such as adding to 'package-directory-list'.

If you’re on a single user system like your laptop or home computer, this is unlikely to matter much to you.

New User Lisp directory feature.
If you have a subdirectory "user-lisp/" in your Emacs configuration
directory, then Lisp files in it and any subdirectories are now
recursively byte-compiled, scraped for autoload cookies and added to
'load-path'.

You can disable the feature by setting 'user-lisp-auto-scrape' to nil,
and you can customize the option 'user-lisp-directory' to process some
other directory instead.  There is also a new command
'prepare-user-lisp' that you can invoke at any time.  See the Info node
"(emacs) User Lisp Directory" for more details.

Oh this is so useful. I have been cargo culting the same snippets of code around for 23 years to load directories with my stuff in it; yes use-package helps but it’s still a lot of manual hassle. About time!

The first client frame now shows warnings from daemon startup.
When there are warnings emitted during Emacs startup, usually due to
problems in your initialization file, these are shown in a "*Warnings*"
buffer.  Until now such warnings were not made visible in the case that
Emacs was started as a daemon.  Now the first frame after daemon startup
will show the "*Warnings*" buffer.  So for example, starting Emacs with
a command like 'emacsclient -a "" -c' will now show "*Warnings*" just
like a plain invocation of 'emacs' would.

Bad news. Emacs’s insistence on telling you about every minor stubbed toe in some random package will now plague you even if you’re running Emacs as a daemon. Such a cursed feature. Nobody cares. If it was important it’d be an error.

Changes in Emacs 31.1

'line-spacing' now supports specifying spacing above the line.
Previously, only spacing below the line could be specified.  The user
option can now be set to a cons cell to specify spacing both above and
below the line, which allows you to vertically center text.

This is a global value to all of Emacs, it’s not a face setting, so you cannot use M-x customize-face to change it. Set it with setopt or customize ui.

New face 'margin' for the window margin display.
A new basic face 'margin' is used by default for text displayed in the
left and right margin areas, which are used by various packages for
per-line annotations.  Its background defaults to the frame default
background, so existing behavior is unchanged for users who do not
customize this new face.

Display strings shown in the margins now inherit unspecified face
attributes from the 'margin' face, if the string itself does not fully
specify its face.  If your code relied on the face of the underlying
buffer text to serve as a default for any unspecified face attributes of
strings displayed in the margin, you must now apply those face
attributes to the margin string itself using 'propertize'.

'prettify-symbols-mode' attempts to ignore undisplayable characters.
Previously, such characters would be rendered as, e.g., white boxes.

'standard-display-table' now has more extra slots.
'standard-display-table' has been extended to allow specifying glyphs
that are used for borders around child frames and menu separators on TTY
frames.

Call the command 'standard-display-unicode-special-glyphs' to set up the
'standard-display-table's extra slots with Unicode characters.  See the
documentation of that command to see which slots of the display table it
changes.

Child frames are now supported on TTY frames.
This supports use-cases like Posframe, Corfu, and child frames acting
like tooltips.  To enable tooltips on TTY frames, call 'tty-tip-mode'.

The presence of child frame support on TTY frames can be checked with
'(featurep 'tty-child-frames)'.

Recent versions of Posframe and Corfu are known to use child frames on
TTYs if they are supported.

This is a welcome change for terminal users. Frames in the terminal do not work as they do in GUI — they behave more like tmux/screen “windows”. Here child frames are just inset popups like the ones you find in GUI Emacs.

Several font-lock face variables are now obsolete.
The following variables are now obsolete: 'font-lock-builtin-face',
'font-lock-comment-delimiter-face', 'font-lock-comment-face',
'font-lock-constant-face', 'font-lock-doc-face',
'font-lock-doc-markup-face', 'font-lock-function-name-face',
'font-lock-keyword-face', 'font-lock-negation-char-face',
'font-lock-preprocessor-face', 'font-lock-string-face',
'font-lock-type-face', 'font-lock-variable-name-face', and
'font-lock-warning-face'.

These variables contributed both to confusion about the relation between
faces and variables, and to inconsistency when major mode authors used
one or the other (sometimes interchangeably).  We always recommended
using faces directly, and not creating variables going by the same name.

If you have customized these variables, you should now customize the
corresponding faces instead, using something like:

    M-x customize-face RET font-lock-string-face RET

If you have been using these variables in Lisp code (for example, in
font-lock rules), simply quote the symbol, to use the face directly
instead of its now-obsolete variable.

Note this is not about the faces but about variables named the same as the faces. Yeah that is confusing. Emacs has faces like font-lock-string-face that you probably have customized already. But it also has variables named the same as the faces. The variables are deprecated.

If you have configured your faces with M-x customize-face (you should!) you have nothing to worry about.

New char-table 'special-mirror-table' for mirroring special glyphs.
This char-table is used to mirror special glyphs (truncation and
continuation) when the user has defined an alternative representation
for those characters via display tables.

find-func.el commands now have history enabled.
The 'find-function', 'find-library', 'find-face-definition', and
'find-variable' commands now allow retrieving previous input using the
usual minibuffer history commands.  Each command has a separate history.

Huh. I never noticed they did not have their own history; now they do. That is good to know I guess but unlikely to affect me much.

New minor mode 'find-function-mode' replaces 'find-function-setup-keys'.
The new minor mode defines the keys at a higher precedence level than
the old function, one more usual for a minor mode.  To restore the old
behavior, customize 'find-function-mode-lower-precedence' to non-nil.

You’re unlikely to have much of a need to customize this.

'find-function' can now find 'cl-defmethod' invocations inside macros.

New minor mode 'prettify-special-glyphs-mode'.
The new minor mode prettifies the special character glyphs (truncation
and continuation) on TTY frames (and GUI frames without fringes).  You
can customize the associated new face 'special-glyphs'.

Minibuffer and Completions

Support for immediate display of the "*Completions*" buffer.
Whenever a minibuffer with completion is opened, then if the completion
table sets the 'eager-display' completion property to non-nil, the
"*Completions*" buffer will now be displayed immediately.  This property
can be overridden for different completion categories by customizing
'completion-category-overrides'.  Alternatively, the new user option
'completion-eager-display' can be set to t to force eager display of
"*Completions*" for all minibuffers, or nil to suppress this for all
minibuffers.

Support for updating "*Completions*" as you type.
If the "*Completions*" buffer is displayed and the completion table sets
the completion property 'eager-update' to non-nil, then the
"*Completions*" buffer will be updated as you type.  This property can
be overridden for different completion categories by customizing
'completion-category-overrides'.  Alternatively, the new user option
'completion-eager-update' can be set to t to make "*Completions*" always
be updated as you type, or nil to suppress this always.  Note that for
large or inefficient completion tables, this can slow down typing.

'RET' chooses the completion selected with 'M-<UP>/M-<DOWN>'.
If a completion candidate is selected with 'M-<UP>' or 'M-<DOWN>',
typing 'RET' will exit completion with that candidate as the result.
This works both in minibuffer completion and for in-buffer completion.
This feature supersedes 'minibuffer-completion-auto-choose', which
previously provided similar behavior; that variable is now nil by
default.

This goes hand in hand with the changes in Emacs 30.1 to make Emacs’s minibuffer completion system behave a little bit more like traditional company/corfu-style completers.

I really rate these new inclusions but I do warn they require a fair bit of customization to really get them to behave like something that does not get in your way.

Support for completion category inheritance.
You can now define completion categories that inherit properties from
existing categories, using the new function 'define-completion-category'.

New optional value of 'minibuffer-visible-completions'.
If the value of this option is 'up-down', only the '<UP>' and '<DOWN>'
arrow keys move point between candidates shown in the "*Completions*"
buffer display, while '<RIGHT>' and '<LEFT>' arrows move point in the
minibuffer.

New user option 'completion-pcm-leading-wildcard'.
This option configures how the partial-completion style does completion.
It defaults to nil, which preserves the existing behavior.  When it is
set to t, the partial-completion style behaves more like the substring
style, in that the input can match a candidate anywhere in the candidate
string.

Another minor tweak to a completion style to make it behave more like something it once did. Emacs has a diverse set of completion styles. The default have changed a lot over the years, sometimes to the chagrin of people who were used to the quirks of a now-relegated default style. For example there’s both an emacs21 and an emacs22 completion style in completion-styles-alist. But see Understanding Minibuffer Completion for more information.

'completion-styles' now can contain lists of bindings.
In addition to a symbol naming a completion style, an element of
'completion-styles' can now be a list of the form '(STYLE ((VARIABLE
VALUE) ...))' where STYLE is a symbol naming a completion style.
VARIABLE will be bound to VALUE (without evaluating it) while the style
is executing.  This allows multiple references to the same style with
different values for completion-affecting variables like
'completion-pcm-leading-wildcard' or 'completion-ignore-case'.  This
also applies to the styles configuration in
'completion-category-overrides' and 'completion-category-defaults'.

Oh man. That is niche. completion-styles is a shopping list of how Emacs must match things in stuff like the minibuffer’s completer. Now you can make it so initials ignores case but substring does not.

Navigating "*Completions*" now accommodates 'completions-format'.
When 'completions-format' is set to 'vertical', typing 'n', 'TAB' or
'M-<DOWN>' in the "*Completions*" buffer (the latter also in the
minibuffer) now moves point to the completion candidate in the next line
in the current column, and wraps to the next column after the last
completion candidate of the current column.  Likewise, typing 'p',
'S-TAB' or 'M-<UP>' moves point to the completion candidate in the
previous line or wraps to the previous column.  Previously, these keys
ignored the vertical format, i.e., they moved point only to the item in
the same line of the next or previous column, in accordance with the
default horizontal format.  In the vertical format, typing '<LEFT>' and
'<RIGHT>' in the "*Completions*" buffer (and when
'minibuffer-visible-completions' is non-nil, also in the minibuffer)
moves point only within the current line, analogously to how, in the
horizontal format, '<DOWN>' and '<UP>' move point only within the
current column.

You’ll want to configure this for sure if you are intent on using the Completions buffer and window for in-buffer completion. I always found navigating between the tabular structure in completions to be a bit weird and offputting; it’s a good use of space, for sure, but a flat list of matches is much easier to reason about.

Selected completion candidate is preserved across "*Completions*" updates.
When the window point is on a completion candidate in the
"*Completions*" buffer (because of 'minibuffer-next-completion' or for
any other reason), it will remain on that candidate after the
"*Completions*" is updated with a new list of completions.  The
candidate is deselected when the "*Completions*" buffer is hidden.

"*Completions*" is now displayed faster when there are many candidates.
As before, if there are more completion candidates than can be displayed
in the current frame, only a subset of the candidates is displayed.
This process is now faster: only that subset of the candidates is
actually inserted into "*Completions*" until you run a command which
interacts with the text of the "*Completions*" buffer.  This
optimization only applies when 'completions-format' is 'horizontal' or
'one-column'.

New user option 'crm-prompt' for 'completing-read-multiple'.
This option configures the prompt format of 'completing-read-multiple'.
By default, the prompt indicates to the user that the completion command
accepts a comma-separated list.  The prompt format can include the
separator description and the separator string, which are both stored as
text properties of the 'crm-separator' regular expression.

It’s a pretty rare feature, that. You can “toggle-select” multiple matches from the minibuffer; few things use it, to be honest. I find the user experience rather poor if I am perfectly honest, no matter the completer. Helm is one of the few tools I think that does it well.

For a practical example of multi-select see Fuzzy Finding with Emacs Instead of fzf.

New user option 'completion-preview-sort-function'.
This option controls how Completion Preview mode sorts completion
candidates.  If you use this mode together with an in-buffer completion
popup interface, such as the interfaces that the GNU ELPA packages Corfu
and Company provide, you can set this option to the same sort function
that your popup interface uses for a more integrated experience.

('completion-preview-sort-function' was already present in Emacs 30.1,
but as a plain Lisp variable, not a user option.)

New user option 'completion-preview-inhibit-functions'.
This option provides fine-grained control over Completion Preview mode
activation.  You can use it to specify arbitrary conditions in which to
inhibit the mode's operation.

Another thing you’ll want to customize. You may want certain movement commands like those used in paredit or combobulate commands to not trigger the completion window.

New mode 'minibuffer-nonselected-mode'.
This mode, enabled by default, directs attention to the active
minibuffer window in the case the minibuffer window is no longer
selected, but still waiting for input.  This uses the new
'minibuffer-nonselected' face.

I like this. I am glad it is enabled by default; it can be a little bit confusing not having a selected/non-selected state.

'read-multiple-choice' now uses the minibuffer to read a character.
It still can use 'read-key' when the variable
'read-char-choice-use-read-key' is non-nil.

'map-y-or-n-p' now uses the minibuffer to read a character.
It still can use 'read-key' when the variable
'y-or-n-p-use-read-key' is non-nil.

Ugh. They mucked around with the default method used for answering “yes or no” prompts in Emacs to make it more like a regular minibuffer thing instead and it caught me out by surprise some years ago when they did that, and it was a pain to track down. Keep you eye on this one if you’re of a similar mind to me on this.

'flex' completion style rewritten to be faster and more accurate.
Completion and highlighting use a new, superior algorithm.  For example,
pattern "scope" now ranks 'elisp-scope-*' functions well above
'dos-codepage' and 'test-completion'.  Pattern "botwin" finds
'menu-bar-bottom-window-divider' before 'ibuffer-other-window'.

Flex matching is an ido-mode feature, and I believe this is strictly speaking a reimplementation of it for the fido-mode completer built on the “new” minibuffer completion system. See Introduction to Ido Mode for IDO mode; and Understanding Minibuffer Completion for the latter.

Mouse

New mode 'mouse-shift-adjust-mode' extends selection with 'S-<mouse-1>'.
When enabled, you can use the left mouse button with the '<Shift>' modifier
to extend the boundaries of the active region by dragging the mouse pointer.

Cool. I rarely drag-select stuff in Emacs, but for finicky stuff it does actually work faster than a keyboard if it’s a one-off.

'context-menu-mode' now includes a "Send to..." menu item.
The menu item enables sending current file(s) or region text to external
(non-Emacs) applications or services.  See send-to.el for customizations.

Oh my this is great. M-x context-menu-mode itself is a reasonably new feature itself (Emacs 28) and is not on by default. It adds contextual right-click menus to stuff. I have not kept abreast with all the places it has had custom commands added to it, and as the default is a bit… barebones, I can imagine most people bounced right off.

You can manually trigger the context menu mode (minor mode active or not) with M-x context-menu-open.

The mouse now drags lines in character increments again.
Dragging a horizontal or vertical line like the mode line or the lines
dividing side-by-side windows now happens in increments of the
corresponding frame's character size again.  This is the behavior
described in the manual and was the default behavior before
'window-resize-pixelwise' was added for Emacs 24.1.  To drag in pixel
increments, as with Emacs 24 through Emacs 30, customize
'window-resize-pixelwise' to t.

Windows

New commands to modify window layouts of frames.
'window-layout-rotate-clockwise' ('C-x w r <RIGHT>') and its counterpart
'window-layout-rotate-anticlockwise' ('C-x w r <LEFT>') rotate an entire
window layout.
'window-layout-flip-topdown' ('C-x w f <DOWN>', 'C-x w f <UP>') and
'window-layout-flip-leftright' ('C-x w f <LEFT>', 'C-x w f <RIGHT>')
flip the window layout vertically and horizontally.
'window-layout-transpose' ('C-x w t') reorganizes windows such that
every horizontal split becomes a vertical split and vice versa.
'rotate-windows' ('C-x w o <RIGHT>') and its counterpart
'rotate-windows-back' ('C-x w o <LEFT>') rotate windows in cyclic
ordering.

Oh I love this. But I’ll probably just pick one direction, clockwise or whatever, and bind that to an easy-to-reach key and suffer the indignity of tapping a few times. It is not often I wish to do this sort of thing. I’m a bit curious though because I am guessing the implementation will cycle through all nodes (Emacs’s window tiling window splits are represented as a tree structure) in the tree — try M-: (window-tree) to see the internal representation.

New user option 'rotate-windows-change-selected'.
This controls whether 'rotate-windows' and 'rotate-windows-back' change
the selected window.  If nil, the selected window does not change.
The default is t, which means the new selected window will be the one
that winds up at the location of the previously-selected window.

Rotate windows but not move with it? Not for me, thanks.

New user option 'transpose-dedicated-windows'.
This controls how functions transposing or rotating windows handle
dedicated windows.  The default is nil, which causes these function to
signal an error if they encounter a dedicated window.

Yeah you’ll want this at nil; dedicated windows are sticky windows. Rotating them around is probably not what you intend — or maybe it is, if you have a peculiar workflow.

Windmove commands now move to skipped windows if invoked twice in a row.
The new user option 'windmove-allow-repeated-command-override' controls
this behavior: if it is non-nil, invoking the same windmove command twice
overrides the 'no-other-window' property, allowing navigation to windows
that would normally be skipped.  The default is t; customize it to nil
if you want the old behavior.

C-x o taps through windows as you probably know. But you can flag a window (see Demystifying Emacs’s Window Manager) as no-other-window so it is exempt from that command. Windmove of course lets you move between windows using your arrow keys.

New hook 'window-deletable-functions'.
This abnormal hook gives its client a way to save a window from being
deleted implicitly by functions like 'kill-buffer', 'bury-buffer' and
'quit-restore-window'.

Emacs always had a weird, disconnected relationship between buffers and windows, as anybody who has ever tried to tame the window manager (see previously mentioned article) so this feels like another patch on top of what is a pretty irreconcilable problem: how do you keep two things that can be interchanged easily from manipulating something the user/package does not want it to? With more hooks, it seems…

Buffer-local window change functions now run in their buffers.
Running the buffer-local version of each of the abnormal hooks
'window-buffer-change-functions', 'window-size-change-functions',
'window-selection-change-functions' and 'window-state-change-functions'
will make the respective buffer temporarily current while running the
hook.

'window-buffer-change-functions' is run for removed buffers too.
The buffer-local version of 'window-buffer-change-functions' may now be
run twice: once for the buffer removed from the window and once for the
buffer now shown in that window.

New user option 'quit-window-kill-buffer'.
This option specifies whether 'quit-window' should preferably kill or
bury the buffer shown by the window to quit.  The default is nil.
Customize it to t to always kill the buffer; customize to a list of
major modes to kill if the buffer's major mode is one of those.

New user option 'kill-buffer-quit-windows'.
This option has 'kill-buffer' call 'quit-restore-window' to handle the
further destiny of any window showing the buffer to be killed.

'split-window' can optionally resurrect deleted windows.
A new optional argument REFER of 'split-window' makes it possible to,
instead of making a new window object, reuse an existing, deleted one.
This can be used to preserve the identity of windows when swapping or
transposing them.

New window parameter 'quit-restore-prev'.
This parameter is set up by 'display-buffer' when it detects that the
window used already has a 'quit-restore' parameter.  Its presence gives
'quit-restore-window' a way to undo a sequence of buffer display
operations more intuitively.

'quit-restore-window' handles new values for BURY-OR-KILL argument.
The values 'killing' and 'burying' are like 'kill' and 'bury' but assume
that the actual killing or burying of the buffer is done by the caller.

New user option 'quit-restore-window-no-switch'.
With this option set, 'quit-restore-window' will delete its window more
aggressively rather than switching to some other buffer in it.

Ahem yeah - as above. All these things are just ointment balmed on Emacs to try and solve an intractable problem. If you let a window host anything, and a buffer jump around and open anywhere (either mechanically or by the whim of the user) then… how do you lock it down properly if you want something IDE-like?

I like the idea of these things. And I predict few will ever really make use of them, even in packages.

The user option 'display-comint-buffer-action' has been removed.
It has been obsolete since Emacs 30.1.  Use '(category . comint)'
instead.  Another user option 'display-tex-shell-buffer-action' has been
removed too, for which you can use '(category . tex-shell)'.

Nothing much to worry about.

New user option 'split-window-preferred-direction'.
Functions called by 'display-buffer' split the selected window when they
need to create a new window.  A window can be split either vertically
(one below the other) or horizontally (side by side).  This new option
determines which direction will be tried first in the case that both
directions are possible according to the values of
'split-width-threshold' and 'split-height-threshold'.  The default value
is 'longest', which means to prefer to split horizontally if the
window's frame is a "landscape" frame, and vertically if it is a
"portrait" frame.  (A frame is considered to be portrait if its vertical
dimension in pixels is greater or equal to its horizontal dimension,
otherwise it is considered to be landscape.)  Previous versions of Emacs
always tried to split vertically first, so to get the previous behavior,
you can customize this option to 'vertical'.  The value 'horizontal'
always prefers the horizontal split.

Good news if you hated the random nature of window splits. Now you’ll have a little bit of control over which direction at least. I recommend you make a note of this and if you find it aggravating that it splits things the wrong way, do set it.

The default value of 'split-width-threshold' is reduced from 160 to 150.
We believe that, after splitting, text filled to 75 columns remains
comfortable to read.

No arguments here.

New optional argument INDIRECT for 'get-buffer-window-list'.
With this argument non-nil, 'get-buffer-window-list' will include in the
return value windows whose buffers share their text with BUFFER-OR-NAME.

New 'display-buffer' action alist entry 'reuse-indirect'.
With such an entry, 'display-buffer-reuse-window' may also choose a
window whose buffer shares text with the buffer to display.

Indirect buffers are a power user feature. If you want to do separate things in the same buffer, you can split and “point” your new window to an already-visited buffer in another window, but then you’ll run into awkward things like shared major modes, the point not always remembering the right place you were because of how points and windows work. An indirect buffer points to a base buffer that you clone from; it is the same underlying text, but everything else is separate (like major mode)

New variable 'window-state-normalize-buffer-name'.
When bound to non-nil, 'window-state-get' will normalize 'uniquify'
managed buffer names by removing 'uniquify' prefixes and suffixes.  This
helps to restore window buffers across Emacs sessions.

New action alist entry 'this-command' for 'display-buffer'.
You can use this in 'display-buffer-alist' to match buffers displayed
during the execution of particular commands.

That’s really cool, but will it work well if you trigger stuff through stuff like magit’s gnarly dispatchers or orgs’?

New command 'other-window-backward' ('C-x O').
This moves in the opposite direction of 'other-window' and is for its
default keybinding consistent with 'repeat-mode'.

No more need for using the negative prefix argument to go backwards.

New functions 'combine-windows' and 'uncombine-window'.
'combine-windows' is useful to make a new parent window for several
adjacent windows and subsequently operate on that parent.
'uncombine-window' can then be used to restore the window configuration
to the state it had before running 'combine-windows'.

I wonder how this fits into atomic windows which are another way of ‘combining’ windows. I am sure there is a substantial difference, perhaps because this one is not tied at all to display-buffer-alist.

New function 'window-cursor-info'.
This function returns a vector of pixel-level information about the
physical cursor in a given window, including its type, coordinates,
dimensions, and ascent.

Frames

New function 'frame-deletable-p'.
If this function returns nil, the following call to 'delete-frame' might
fail to delete its argument FRAME or might signal an error.  It is
therefore advisable to use this function as part of a condition that
determines whether to call 'delete-frame'.

New function 'frame-use-time'.
This function is the frame equivalent of the function 'window-use-time'
for a window.  The result is the 'window-use-time' of the frame's most
recently used window.

New functions 'get-mru-frames' and 'get-mru-frame'.
'get-mru-frames' returns a list of frames sorted by their most recent
use time, among all frames, or among those visible or iconified on the
same terminal as the selected frame.  Child frames can be excluded.  A
single frame can be excluded (e.g. the selected frame).  'get-mru-frame'
returns the single most recently used frame.

After deleting, 'delete-frame' now selects the most recently used frame.
Previously, after deleting a specified frame, 'delete-frame' would
select the oldest visible frame on the same terminal.  To revert to the
old behavior, set the new user option 'delete-frame-choose-selected'
to nil.

I am not a massive frame user as I never found the customization to make it work the way I liked it worth the effort, even though I do also use a tiling WM. But returning to the last seen frame does seem like an odd thing to only add now; this will no doubt restore the same of people who prefer frame-only approaches to windows.

New value 'force' for user option 'frame-inhibit-implied-resize'.
This will inhibit implied resizing while a new frame is made.  It can be
useful on tiling window managers where the initial frame size should be
specified by external means.

New user option 'alter-fullscreen-frames'.
This option is useful to maintain a consistent state when attempting to
resize fullscreen frames.  It defaults to 'inhibit' on NS builds which
means that a fullscreen frame will not change size.  It defaults to nil
everywhere else, which means that the window manager is supposed to
either resize the frame and change the fullscreen status accordingly, or
keep the frame size unchanged.  The value t means to first reset the
fullscreen status and then resize the frame.

New functions to set frame size and position in one compound step.
'set-frame-size-and-position' sets the new size and position of a frame
in one compound step.  Both size and position can be specified as with
the corresponding frame parameters 'width', 'height', 'left' and 'top'.
'set-frame-size-and-position-pixelwise' is similar but has a more
restricted set of values for specifying size and position.

New commands 'split-frame' and 'merge-frames'.
'split-frame' moves a specified number of windows from an existing frame
to a newly-created frame.  'merge-frames' merges all windows from two
frames into one of these frames and deletes the other one.

Frames can now be renamed to "F<number>" on text terminals.
Unlike with other frame names, an attempt to rename to "F<number>"
signals an error when a frame of that name already exists.

As I mentioned earlier frames in terminal Emacs are really just another way of doing a window configuration / screen-style “window pane”.

New frame parameters 'cloned-from' and 'undeleted'.
The frame parameter 'cloned-from' is set to the frame from which the new
frame is cloned using the command 'clone-frame'.

The frame parameter 'undeleted' is set to t when a frame is undeleted
using the command 'undelete-frame'.

These are useful if you need to detect a cloned or undeleted frame in
hooks like 'after-make-frame-functions' and
'server-after-make-frame-hook'.

Frames now have unique ids and the new function 'frame-id'.
Each non-tooltip frame is assigned a unique integer id.  This allows you
to unambiguously identify frames even if they share the same name or
title.  When 'undelete-frame-mode' is enabled, each deleted frame's id
is stored for resurrection.  The function 'frame-id' returns a frame's
id (in C, use the frame struct member 'id').

New commands 'select-frame-by-id', 'undelete-frame-by-id'.
The command 'select-frame-by-id' selects a frame by ID and undeletes it
if deleted.  The command 'undelete-frame-by-id' undeletes a frame by its
ID.  When called interactively, both functions prompt for an ID.

Mode Line

New definitions for mode line faces on dark backgrounds.
The faces 'mode-line' and 'mode-line-highlight' now have separate
definitions for dark backgrounds.  Previously, these two faces looked
the same with both light and dark background modes.  To get the previous
visuals for these two faces, customize them to have the colors "grey75"
and "grey40", respectively, regardless of the background mode.

New user option 'mode-line-collapse-minor-modes'.
This is a new, built-in facility to hide minor mode lighters.  If
non-nil, minor mode lighters on the mode line are collapsed into a
single button.  The value can also be a list to specify minor mode
lighters to hide or show.  The default value is nil, which retains the
previous behavior of showing all minor mode lighters.

One of my earliest articles was Hiding and replacing modeline strings with clean-mode-line. It’s been an issue as long as mode authors have had a say in how loud their mode line lighters should be.

Glad it is finally built in. No word on whether it plugs into :delight / :diminish in use-package.

New user option 'mode-line-modes-delimiters'.
This option allows changing or removing the delimiters shown around
the major mode and list of minor modes in the mode line.  The default
retains the existing behavior of using parentheses.

New minor mode 'mode-line-invisible-mode'.
This minor mode makes the mode line of the current buffer invisible.
The command 'mode-line-invisible-mode' toggles the visibility of the
current-buffer's mode line.  The default is to show the mode line of
every buffer.

People do ask for this all the time, so it’s good to see a built in feature to do this instead of all the hacky tricks people got up to before.

The standard mode line no longer specifies minimum widths.
The default values for the 'mode-line-position' variable and
'mode-line-format' user option no longer specify any minimum widths.  If
you use a proportional font for your mode line, you may need to
customize the values of these variables to include minimum widths again.

Tab Bars and Tab Lines

Tab bars are window configurations you switch between; tab lines are like browser tabs that point to buffers in the window.

New commands 'split-tab' and 'merge-tabs'.
'split-tab' moves a specified number of windows from an existing tab to
a newly created tab.  'merge-tabs' merges all windows from two tabs into
one of these tabs, and closes the other.

New abnormal hook 'tab-bar-auto-width-functions'.
This hook allows you to control which tab-bar tabs are auto-resized.

'mouse-face' properties are now supported on the 'tab-bar'.
'tab-bar' tab buttons are now highlighted when the mouse pointer
hovers over them.  You can customize the new face
'tab-bar-tab-highlight'.

New abnormal hook 'tab-bar-post-undo-close-tab-functions'.
This hook allows you to operate on a reopened tab.

This is useful when you define custom tab parameters that may need
adjustment when a tab is restored, without resorting to advice.

I do actually end up closing tab bar tabs by mistake quite often. And it has had an undo feature C-x t u to fix screwups like that for a long time now.

Tabs are now closed upon releasing the middle mouse button.
Previously, closing the tab-bar's tabs occurred upon pressing the
button.

New user option 'tab-bar-define-keys'.
This controls which key bindings tab-bar creates.  Values are t, the
default, which defines all keys and is backwards compatible, 'numeric'
for tab number selection only, 'tab' for the 'TAB' and 'S-TAB' keys
only, and nil for none.

This is useful to avoid key binding conflicts, such as when folding in
outline mode using 'TAB' keys, or when a user wants to define her own
tab-bar keys without first having to remove the defaults.

New variable 'tab-bar-format-tab-help-text-function'.
This variable may be overridden with a user-provided function to
customize the help text for tabs displayed on the tab-bar.  Help text is
normally shown in the echo area or via tooltips.  See the variable's
docstring for the arguments passed to a help-text function.

New variable 'tab-bar-truncate'.
When non-nil, it truncates the tab bar, and therefore prevents
wrapping and resizing the tab bar to more than one line.

New user option 'tab-line-define-keys'.
When t, the default, it redefines window buffer switching keys
such as 'C-x <LEFT>' and 'C-x <RIGHT>' to tab-line specific variants
for switching tabs.

New command 'tab-line-move-tab-forward' ('C-x M-<RIGHT>').
Together with the new command 'tab-line-move-tab-backward'
('C-x M-<LEFT>'), it can be used to move the current tab
on the tab line to a different position.

New command 'tab-line-close-other-tabs'.
It is bound to the tab's context menu item "Close other tabs".

New user option 'tab-line-exclude-buffers'.
This user option controls where 'tab-line-mode' should not be enabled in
a buffer.  The value must be a condition which is passed to
'buffer-match-p'.

New user option 'tab-line-close-modified-button-show'.
With this user option, if non-nil (the default), the tab close button
will change its appearance if the tab's selected buffer has been
modified.

New user option 'tab-line-tabs-window-buffers-filter-function'.
This user option controls which buffers should appear in the tab line.
By default, this is set so as to not filter out any buffers.

Aha this is useful. One problem with tab line is that it’s quite indiscriminate; it won’t show hidden buffers by default (they start with a whitespace) obviously but it’s still a bit heavyhanded. Now you can at least limit what you see.

New faces 'tab-line-active' and 'tab-line-inactive'.
These inherit from the 'tab-line' face, but the faces actually used on
the tab lines are now these two: the selected window uses
'tab-line-active', and non-selected windows use 'tab-line-inactive'.

Help

New binding 'C-h u' for 'apropos-user-option'.

IDLWAVE has moved to GNU ELPA.
The version included with Emacs is out-of-date, and is now marked as
obsolete.  Use 'list-packages' to install the 'idlwave' package from GNU
ELPA instead.

New faces 'header-line-active' and 'header-line-inactive'.
These inherit from the 'header-line' face, but the faces actually used
on the header lines are now these two: the selected window uses
'header-line-active', and non-selected windows use 'header-line-inactive'.

Useful; header line is an immovable header that appears at the top of a window. It is commonly used for things like column headers in tables, as seen in M-x list-packages.

In 'customize-face', the "Font family" attribute now supports completion.

Heavenly manna indeed. I have long argued that all this complex futzing around with .Xresources, frame-setting faces and all manner of complicated ways of setting your default font is a bad habit and that M-x customize-face RET default RET is the simplest and most effective compared to the alternatives. Well, you don’t have to guess at the names of fonts any more! Emacs is finally capable of auto completing them. Excellent change.

'process-adaptive-read-buffering' is now nil by default.
Setting this variable to a non-nil value reduces performance and leads
to wrong results in some cases.  We believe that it is no longer useful;
please contact us if you still need it for some reason.

Another toggle switch to maybe possibly potentially speed Emacs up a tad; it’s part of a growing list of these magic feature toggles that may or may not have adverse consequences down the road. I checked my Emacs and mine is set to nil. I do not recall why I set it to nil, nor can I remember when.

'byte-compile-cond-use-jump-table' is now obsolete.

Modified settings for an enabled theme now apply immediately.
Evaluating a 'custom-theme-set-faces' or 'custom-theme-set-variables'
call for an enabled theme causes the settings to apply immediately,
without a need to re-load the theme.

'describe-variable' now automatically says if 'setopt' is needed.
If a user option has a defcustom ':set' function, users will normally
need to set it with 'setopt' for it to take an effect.  If the docstring
doesn't already mention 'setopt', the 'describe-variable' command will
now add a note about this automatically.

One of the greatest challenges in Emacs is convincing people - including yours truly - to stop using setq to bind values to global/customizable variables. Emacs’s customize system – defined as anything you can edit with M-x customize – supports edge triggers: code that runs when one of its variables change. It was once uncommon enough that nobody really had to worry; more and more things in Emacs lean into this system though.

The primary reason people use setq is that it just kinda-sorta works (notwithstanding the edge-trigger) but also because the proper way to set variables via customize’s machinery is custom-set-variables which is an obnoxious utility function that not only has a bad prefix namespace custom vs customize but also it’s just so damn long to type.

So nobody bothered to use it. Emacs 29.1 added setopt which automatically does all the heavy lifting and it’s a drop-in replacement for setq.

New user option 'eldoc-help-at-pt' to show help at point via ElDoc.
When enabled, display the 'help-at-pt-kbd-string' via ElDoc.  This
setting is an alternative to 'help-at-pt-display-when-idle'.

Eldoc is Emacs’s help/document/code argument lookup system that actives when you move point around. It relies on a complex timing machinery to trigger the help. Forcing it to appear at point (even if that is nearly always your current point) is a great utility function. Now you can have eldoc without the timer: bind it to a key when you need it and off it goes.

New user option 'native-comp-async-on-battery-power'.
Customize this to nil to disable starting new asynchronous native
compilations while AC power is not connected.

Somewhere someone with a laptop more dinged-up than Zildjian cymbal lost their last 5% of battery to native comp and furiously decided to solve this problem once and for all.

New user option 'show-paren-not-in-comments-or-strings'.
If this option is non-nil, it tells 'show-paren-mode' not to highlight
parens inside comments and strings.  If set to 'all', 'show-paren-mode'
will never highlight parens that are inside comments or strings.  If set
to 'on-mismatch', mismatched parens inside comments and strings will not
be highlighted.  If set to nil (the default), highlight parens wherever
they are.

Show paren of course is Emacs paren highlighter, though its name today is doing it a disservice as it is designed to highlight like terms like braces, string quotes or things like begin and end terms.

New user option 'view-lossage-auto-refresh'.
If this option is non-nil, the lossage buffer of 'view-lossage' will be
refreshed automatically for each new input keystroke and command
invoked.

Lossage is C-h l and it reflects the last N number of typed keys in your Emacs. With auto-refresh enabled you can simulate basic version of those “keypress overlays” people use in streaming videos. Useful for gifs too!

Change in SVG foreground color handling.
SVG images no longer have the 'fill' attribute set to the value of
':foreground' or the current text foreground color.  The 'currentcolor'
CSS attribute is still set, as before.

This change should result in more consistent display of SVG images.

To use the ':foreground' or current text color ensure the 'fill' attribute
in the SVG is set to 'currentcolor', or set the image spec's ':css'
value to 'svg {fill: currentcolor;}'.

Errors signaled by 'emacsclient' connections can now enter the debugger.
If 'debug-on-error' is non-nil, errors signaled by Lisp programs
executed by 'emacsclient' connections will now enter the Lisp debugger
and show a backtrace.  If 'debug-on-error' is nil, these errors will be
sent to 'emacsclient', as before, and will be displayed on the terminal
from which 'emacsclient' was invoked.

Empty string arguments to emacsclient are no longer ignored.
Emacs previously discarded arguments to emacsclient of zero length, such
as in 'emacsclient --eval "(length (pop server-eval-args-left))" ""'.
These are no longer discarded.

Huh. That may have explained some weird issues I’ve run into calling evals into emacsclient over the years. I always just assumed I did something wrong!

Emacs now uses the 'setrgbf' and 'setrgbb' terminfo capabilities.
Emacs now uses 24-bit colors on terminals that support the 'setrgbf' and
'setrgbb' user-defined terminfo capabilities.  These are supported by
more terminals and applications than the old capabilities, 'setf24' and
'setb24', which are now obsolete.

I’m not an expert on termcaps so I cannot say what these caps offer people, but Emacs already supports 24-bit if you did not know. In fact, you can just set the environment variable COLORTERM=truecolor to force Emacs to treat your terminal as 24-bit capable.

New user option 'xterm-update-cursor' to update cursor display on TTYs.
When enabled, Emacs sends Xterm escape sequences on Xterm-compatible
terminals to update the cursor's appearance.  Emacs can update the
cursor's shape and color.  For example, if you use a purple bar cursor
on graphical displays then when this option is enabled Emacs will use a
purple bar cursor on compatible terminals as well.  See the Info node
"(emacs) Cursor Display" for more information.

Neat. The highlight of course being that Emacs has multiple cursor styles. See M-x customize-option cursor-type.

New command 'copy-theme-options'.
You can use this command to copy options from a theme into your user
configuration.

New user option 'multiple-terminals-merge-keyboards'.
Customizing this option to non-nil disables entering single-keyboard
mode in most cases in which Emacs would by default enter that mode.
This can make things work better for some cases of X forwarding; see the
Info node "(emacs) Multiple Displays".

Emacs now comes with Org v9.8.
See the file "etc/ORG-NEWS" for user-visible changes in Org.

New user option 'compilation-search-extra-path'.
compile.el will now use paths specified in both
'compilation-search-extra-path' and 'compilation-search-path' when
searching.  'compilation-search-extra-path' is consulted first.  One
possible use case for this option is to add new search paths on a
per-project basis with directory-local variables.

Editing Changes in Emacs 31.1

Commands for keyboard translation.
'key-translate' is now interactive.  It prompts for a key to translate
from, and another to translate to, and sets 'keyboard-translate-table'.
The new command 'key-translate-remove' prompts for a key/translation
pair, with 'completing-read', and removes the translation from the
translation table.

My article on Mastering Key Bindings in Emacs is a good place to start on key bindings.

But it is not a good article to understand keyboard translation. Even I am not crazy enough to try to write an article that explains that. I spent nearly a full day trying to trace a weird keyboard translation issue in Combobulate that only manifests in some terminals with some key bindings and only in Combobulate’s complicated “carousel interface”.

The translation system – and how it plugs into your OS, tty, etc. – and trying to fully understand it will make you go crazy.

Internationalization

Emacs now supports Unicode Standard version 17.0.

New input method 'greek-polytonic'.
This input method has support for polytonic and archaic Greek
characters.

New language environment and input method for Tifinagh.
The Tifinagh script is used to write the Berber languages.

New input methods for Northern Iroquoian languages.
Input methods are now implemented for Haudenosaunee languages in the
Northern Iroquoian language family: 'mohawk-postfix' (Mohawk
[Kanien’kéha / Kanyen’kéha / Onkwehonwehnéha]), 'oneida-postfix' (Oneida
[Onʌyote’a·ká· / Onyota’a:ká: / Ukwehuwehnéha]), 'cayuga-postfix'
(Cayuga [Gayogo̱ho:nǫhnéha:ˀ]), 'onondaga-postfix' (Onondaga
[Onųdaʔgegáʔ]), 'seneca-postfix' (Seneca [Onödowá’ga:’]), and
'tuscarora-postfix' (Tuscarora [Skarù·ręʔ]).  Additionally, there is a
general-purpose 'haudenosaunee-postfix' input method to facilitate
writing in the orthographies of the six languages simultaneously.

New input methods for languages based on Burmese.
These include: Burmese, Burmese (visual order), Shan, and Mon.

New language environment and input methods for Syriac languages.
A new language environment for languages that use the Syriac script:
Classical Syriac, Aramaic, and others.  There are two new input methods
for these languages: Syriac and Syriac (phonetic).

'visual-wrap-prefix-mode' now supports variable-pitch fonts.
When using 'visual-wrap-prefix-mode' in buffers with variable-pitch
fonts, the wrapped text will now be lined up correctly so that it is
exactly below the text after the prefix on the first line.

Visual wrap prefix mode, not to be confused with truncating long lines (M-x toggle-truncate-lines) or visual line mode (M-x visual-line-mode) deals with text that overflow one line and how it is wrapped. I’m not going to get into which one does what; try them out in turn and see which one works best.

New commands 'unix-word-rubout' and 'unix-filename-rubout'.
Unix-words are words separated by whitespace regardless of the buffer's
syntax table.  In a Unix terminal or shell, 'C-w' kills by Unix-word.
The new commands 'unix-word-rubout' and 'unix-filename-rubout' allow
you to bind keys to operate more similarly to such a terminal.

Emacs having it all, you’d think – especially given its roots – it would already a panoply of methods for doing this.

Honestly even if you’re a die-hard fan of this method of killing I would unlearn that habit. Emacs’s combined system of moving-editing-killing by word and so forth is far superior.

New user option 'kill-region-dwim'.
This option, if non-nil, modifies the fall-back behavior of
'kill-region' ('C-w') if no region is active, and will kill the last
word instead of raising an error.  If you have disabled Transient Mark
mode you might prefer to bind 'unix-word-rubout' to a key instead.

No see this is not the right way forward. C-w and M-w absent a region should kill the current line and copy it respectively. That is a far more sensible approach than fall back to dumb non-TMM behavior as it does pre-Emacs 31.

Here is the code I stole from Emacswiki 20+ years ago to do exactly this. One of my favorite Emacs life hacks:

(defadvice kill-ring-save (before slick-copy activate compile)
  "When called interactively with no active region, copy a single line instead."
  (interactive
   (if mark-active (list (region-beginning) (region-end))
     (list (line-beginning-position)
           (line-beginning-position 2)))))

(defadvice kill-region (before slick-cut activate compile)
  "When called interactively with no active region, kill a single line instead."
  (interactive
   (if mark-active (list (region-beginning) (region-end))
     (list (line-beginning-position)
           (line-beginning-position 2)))))

New user option 'delete-pair-push-mark'.
This option, if non-nil, makes 'delete-pair' push a mark at the end of
the region enclosed by the deleted delimiters.  This makes it easy to
act on that region.  For example, you can highlight it using 'C-x C-x'.

Now this is useful. M-x delete-pair (typically not bound to anything) is a long line of helpful editing commands that, alongside things like M-x raise-sexp do not get their time in the sun as they are unbound by default.

One common problem with deleting a little bit here and a little bit over there is exactly that Emacs does not make it easy to capture the extent over the change that took place. Pushing a mark (Emacs’s little point beacon system) is an obvious choice here.

Electric Pair mode

Electric Pair mode can now pair multiple delimiters at once.
You can now insert or wrap text with multiple sets of parentheses and
other matching delimiters at once with Electric Pair mode, by providing
a prefix argument when inserting one of the delimiters.

Neat but I will never remember this. I do not subscribe to the school of “think before you type” where you count your steps and then use the right numeric argument.

Electric Pair mode now supports multi-character paired delimiters.
'electric-pair-pairs' and 'electric-pair-text-pairs' now allow using
strings for multi-character paired delimiters.

To use this, add a list to both electric pair user options: '("/*" . "*/")'.

You can also specify that an extra space should be inserted after the
first string, like this: '("/*" " */" t)'.

Electric pair is a god-send in that it is a million times better than the hacky skeleton template system most of us lugged around before it became standard in Emacs a long time ago. But once again this is the sort of functionality you’d expect it could already do out of the box. Emacs’s own core is written in C where /* */ is used all the time for comments!

New user option 'electric-indent-actions'.
This user option specifies a list of actions to reindent.  The possible
elements for this list are: 'yank' to reindent the yanked text, and
'before-save' to indent the whole buffer before saving it.

As always, how well this works in whitespace-sensitive languages remains to be seen. I know from experience how difficult it is to corral the indentation engines into handling this well; so for Python and such like it really can’t do much more than fixed indentation.

You can now use 'M-~' during 'C-x s' ('save-some-buffers').
Typing 'M-~' while saving some buffers means not to save the buffer and
also to mark it as unmodified.  This is an alternative way to mark a
buffer as unmodified which doesn't require switching to that buffer.

M-~ generally speaking is a key binding for the “is this buffer modified in Emacs” flag. Most people do not know about this obscure command.

New minor mode 'delete-selection-local-mode'.
This mode sets 'delete-selection-mode' buffer-locally.  This can be
useful for enabling or disabling the features of 'delete-selection-mode'
based on the state of the buffer, such as for the different states of
modal editing packages.

Delete selection mode is how most editors work: you select text, and if you start typing, it is deleted and replaced with what you just typed. In Emacs, you have to enable a mode to get this functionality.

New user option 'exchange-point-and-mark-highlight-region'.
When set to nil, this modifies 'exchange-point-and-mark' so that it doesn't
activate the mark if it is not already active.
The default value is t, which retains the old behavior.
This variable has no effect when Transient Mark mode is off.

I have been cargo culting an advice for this exact misbehavior around for the better part of 15 years. See Fixing the mark commands in transient mark mode.

C-x C-x is another hidden gem in Emacs. Emacs has point (your cursor) and mark (a beacon somewhere in your buffer) and back in the good old days Emacs did not highlight text selections by default. You had to slum it with no visual aid at all: all you had was your mark and point. Sounds bad, but… actually it’s not that big a deal. You generally know where you started your marking and it runs to your point.

Transient-mark-mode (obviously enabled by default… nowadays…) made it so you can see your region selection. However… it did break some useful features in weird ways. When you do M-< and such to move to the beginning or end of a buffer or C-s to start isearch Emacs will set the mark, meaning it effectively sets the start of where a region “is”.

Power users would pick a spot, search or jump or whatever to where they needed to go, and execute a “region” command that would work from where ever their point landed, say the match they picked in C-s for example, all the way back from where they were when they first called C-s. Bam — that was how you acted on a region.

So C-x C-x had really, really important purpose back then: you could swap between the mark and point by exchanging their positions. Great if you just wanted to double check the region you were going to act on; or maybe toggle between where you were/are.

So when you then execute a command (like kill-region) Emacs’s code would – slavishly, laboriously, I might add – always ensure the point and mark were the right way ’round internally, and then just act on that range.

Add highlighting into the mix and now you have a dumb rectangle that follows you along everywhere because C-x C-x would ALSO activate your region marker (C-SPC). So dumb, because it screws up keyboard macros and all sorts. Bleh.

So 15 years ago I made it not do that. And you should, too.

You can now use 'M-s t' to swap FROM and TO during 'query-replace'.
Likewise during 'query-replace-regexp'.  The original binding of 'M-s'
('next-matching-history-element') is now available on 'M-s M-s' or 'M-s
s' for query replace minibuffer input.

Hah. Neat. A few versions ago they made it so various query replace functions emit a special -> sigil to indicate from/to. You could edit the whole string and move stuff around, and now they’ve just added a nice shortcut to make it even easier.

New commands for filling text using semantic linefeeds.
The new command 'fill-paragraph-semlf' fills a paragraph of text using
"semantic linefeeds", where a newline is inserted after every sentence.
The new command 'fill-region-as-paragraph-semlf' fills a region of text
using semantic linefeeds, as if the region were a single paragraph.  You
can set the variable 'fill-region-as-paragraph-function' to the value
'fill-region-as-paragraph-semlf' to make commands like 'fill-paragraph'
and 'fill-region' fill text using semantic linefeeds.

Temporary files are named differently when 'file-precious-flag' is set.
When the user option 'file-precious-flag' is set to a non-nil value,
Emacs now names the temporary file it creates while saving buffers using
the original file name with ".tmp" appended.  Thus, if saving the buffer
fails for some reason, and the temporary file is not renamed back to the
original file's name, and you can easily identify which file's saving
failed.

'C-u C-x .' clears the fill prefix.
You can now use 'C-u C-x .' to clear the fill prefix, similarly to how
you could already use 'C-u C-x C-n' to clear the goal column.

Fill prefix C-x . looks at where your point is on a line and designates everything from point to the beginning of the line as the fill prefix. When you type M-q on a long paragraph it’ll reflow it and insert the fill prefix for each new line. Use cases include prefixing email paragraphs with > or what have you.

Now you can reset it without having to move point to the bol.

New prefix argument for 'C-/' in Dired and Proced modes.
The Dired and Proced major modes bind mode-specific undo commands to the
same keys to which 'undo' is globally bound, 'C-/', 'C-_' and 'C-x u'.
These commands did not previously accept a prefix argument.
Now a numeric prefix argument specifies a repeat count, just like it
already did for 'undo'.

New minor mode 'center-line-mode'.
This mode keeps modified lines centered horizontally according to the
value of 'fill-column', by calling 'center-line' on each non-empty line
of the modified region.

New command 'unfill-paragraph'.
This is the inverse of 'M-q' ('fill-paragraph').

I am pretty sure org mode or something has had this for millennia buried in its codebase somewhere. But yeah, nice I guess.

Changes in Specialized Modes and Packages in Emacs 31.1

Project

Project is Emacs’s latest project management suite in a long line of project suites that ship with Emacs already. It’s nice, you should use it.

New command 'project-root-find-file'.
It is equivalent to running 'project-any-command' with 'find-file'.

New command 'project-customize-dirlocals'.
It is equivalent to running 'project-any-command' with
'customize-dirlocals'.

Improved prompt for 'project-switch-project'.
The prompt now displays the project on which to invoke a command.

'project-prompter' values may be called with up to three arguments.
These allow callers of the value of 'project-prompter' to specify a
prompt string; prompt the user to choose between a subset of all the
known projects; and disallow returning arbitrary directories.
See the docstring of 'project-prompter' for a full specification of
these new optional arguments.

'project-current' has a new optional argument, MAYBE-PROMPT.
If 'project-current' is called with this argument non-nil, then it is
passed to the 'project-prompter' to use as a prompt string.
Callers can use this to indicate the reason for which or context in
which Emacs should ask the user to select a project.

New command 'project-find-matching-buffer'.
It can be used when switching between projects with similar file trees
(such as Git worktrees of the same repository).  It supports being
invoked standalone or from the 'project-switch-commands' dispatch menu.
See also the 'C-x v w w' ('vc-switch-working-tree') command, below.

That is a nice bit of symmetry. I usually switch between worktrees in magit with % g, but I am happy to see project gaining some form of generic support for this concept.

New variable 'project-find-matching-buffer-function'.
Major modes can set this to major mode-specific functions to control how
'project-find-matching-buffer' finds matching buffers.

New user option 'project-list-exclude'.
This user option describes projects that should always be skipped by
'project-remember-project'.

New user option 'project-prune-zombie-projects'.
This user option controls the automatic deletion of projects from
'project-list-file', when prompting for a project, that cannot be
accessed.  The value must be an alist where each element is of the
form:

    (WHEN . PREDICATE)

where WHEN specifies where the deletion will be performed, and PREDICATE
is a function which takes one argument, and must return non-nil if the
project should be removed.

New command 'project-save-some-buffers' bound to 'C-x p C-x s'.
This is like 'C-x s', but only for this project's buffers.

'project-remember-project' is now interactive.

'project-shell' and 'project-eshell' support numeric prefix buffer naming.
They now accept numeric prefix arguments to select or create numbered
shell sessions.  For example, 'C-2 C-x p s' switches to or creates a
buffer named "*name-of-project-shell<2>*".  By comparison, a plain
universal argument as in 'C-u C-x p s' always creates a new session.

'project-switch-to-buffer' re-uniquifies buffer names while prompting.
When 'uniquify-buffer-name-style' is non-nil, 'project-switch-to-buffer'
changes the buffer names to only make them unique within the given
project, during completion.  That makes some items shorter.

'project-switch-to-buffer' uses 'project-buffer' as completion category.
The category defaults are the same as for 'buffer', but any user
customizations need to be re-added.

'project-mode-line' can now show the project name only for local files.
If the value of 'project-mode-line' is 'non-remote', project name and
the Project menu will be shown on the mode line only for projects with
local files.

One common source of performance problems in people’s riced Emacs configs is the mode line, believe it or not. It gets re-rendered more often than you think, and a lot of people cram expensive junk into it that require a file system round-trip. Fine when you’re just looking at stuff on your macbook. But over TRAMP? It’ll kill your performance.

The VC-aware project backend caches the current project and its name.
The duration for which the values are cached depends on whether it is
called from a 'non-essential' context, and is determined by the variables
'project-vc-cache-timeout' and 'project-vc-non-essential-cache-timeout'.

Network Security Manager (NSM)

NSM warns about TLS 1.1 by default.
It has been deprecated by RFC 8996, published in 2021.

NSM warns about DHE and RSA key exchange by default.
Emacs now warns about ephemeral Diffie-Hellman key exchange, and static
RSA key exchange, also when 'network-security-level' is customized to
its default 'medium' value.

Etags

Ctags, Etags, etc. are all a family of source code indexers that pull out semantically important stuff like function names and their precise location

New command-line options for handling unrecognized programming languages.
The new command-line option '--no-fallback-lang' disables attempts to
parse as Fortran or C/C++ files whose programming language 'etags' could
not determine.  This allows avoiding false positives and reduces the
time required to scan directories with many such files.  Another new
option '--no-empty-file-entries' disables generation of file entries in
tags tables for files in which no tags were found.

Delete Selection mode

New face 'delete-selection-replacement' for the replacement text.
This comes with a change to how we track what is considered "the
replacement text", which should be more robust, and is made more clear
by the highlighting.

Editorconfig

'editorconfig-apply' is declared obsolete.
You can now use 'editorconfig-display-current-properties' without having
to call 'editorconfig-apply'.

Auth Source

Auth source is Emacs’s declarative secret store wrapper. I’ve written about it: Keeping Secrets in Emacs with GnuPG and Auth Sources

Non-existing or empty files in 'auth-sources' are ignored.
File-based data stores are ignored in 'auth-sources' if the underlying
data file does not exist.  This is relevant if a new secret is stored in
such a file; the first usable entry of 'auth-sources' is selected as the
target file.  If you want files that do not exist to also be selected,
customize the user option 'auth-source-ignore-non-existing-file' to nil.

'auth-sources' set to nil means use only the password cache.

Autoinsert

Autoinsert – not to be confused with Skeletons, Abbrev, Tempo, etc. – is used to insert text templates when you create new files that match certain file patterns.

New condition for 'auto-insert-alist'.
'auto-insert-alist' can now contain predicates taking no argument as
conditions.  These types of conditions should be declared with
'(predicate FUNCTION)'.  This allows triggering 'auto-insert' with
finer-grained control.

Register

Registers are ephemeral stores of text snippets, window/frame configurations, point locations and much more. They’re designed for fast keyboard access and I use them all the time, especially with keyboard macros.

New commands 'buffer-to-register' and 'file-to-register'.
These allow users to interactively store files and buffers in registers.
Killed buffers stored in a register using 'buffer-to-register' are
automatically converted to a file-query value if the buffer was visiting
a file.

So a bit like bookmarks I guess, which are permanent stores of references to files, info manual locations and much more.

The "*Register Preview*" buffer shows only suitable registers.
That was already the case for the "fancy" UI but is now also true in
the default UI you get, i.e., when 'register-use-preview' is 'traditional'.

The "*Register Preview*" buffer shows sorted items.

Tree-sitter

Tree-sitter is a fancy parsing suite for structured text like code, markdown and so on. I have written an ungodly amount about tree-sitter and also code that interacts with tree-sitter.

See How to Get Started with Tree-Sitter, Combobulate: Structured Movement and Editing with Tree-Sitter, etc. etc. etc.

New user option 'treesit-enabled-modes'.
You can customize it either to t to enable all available
tree-sitter-based modes, or to select a list of tree-sitter-based modes
to enable.  Depending on your customization, it modifies the variable
'major-mode-remap-alist' from the corresponding variable
'treesit-major-mode-remap-alist' prepared by tree-sitter-based mode
packages.

I’ve long complained about the remap system and the fact that tree-sitter modes are often just bare bones reimplementations of their original, non-TS-enabled cousins. But configuring the remap alist was a hassle for beginners so I am happy to see some movement here towards simplifying it.

New user option 'treesit-auto-install-grammar'.
It controls the automatic installation of tree-sitter grammar libraries
needed for tree-sitter-based modes, if these grammar libraries are not
available when such modes are turned on.

About time. Having to lug around dozens of complex git refs to the right, magic version of a tree-sitter library was positively terrible UX for everyone.

Tree-sitter adoption is a tiny fraction of what it should be because of the decision to refuse to keep text strings to github release tags that match precisely what each major mode needs to work.

You see, the poindexters who build tree-sitter the library and the grammars break compatibility all. the. time. So you can’t just pull a new version and expect stuff to work — it will NOT.

This is a good thing indeed. But it’s taken several years and what I imagine are a large amount of reported user bugs for this change to take place.

'treesit-extra-load-path' is now a customizable user option.
The first directory in the list is used as the default directory
to install the language grammar when 'treesit-auto-install-grammar'
is 'ask', 'ask-dir' or 'always'.

'treesit-language-source-alist' supports keywords.
The language and URL are mandatory, but remaining data can use keywords like

    (json "https://github.com/tree-sitter/tree-sitter-json" :commit "4d770d3")

The file treesit-x.el defines a number of simple tree-sitter modes.
Using the new macro 'define-treesit-generic-mode', generic modes are
defined including, but not limited to, 'gitattributes-generic-ts-mode'.
Visiting a file in such mode asks for confirmation before installing
its tree-sitter grammar.  Then it highlights the visited file
according to the syntax defined by the grammar.

Excellent. We already have define-generic-mode in generic.el for quickly throwing a major mode together for simple file formats. Here we can leverage the .scm files tree-sitter grammars often ship with that provide out of the box suggestions for syntax highlighting. Honestly our system in Emacs is way better but… someone has to Write a Tree-Sitter Major Mode first properly to do it the right way. So this is a nice compromise

Indirect buffers can have their own parser list.
Before, indirect buffers share their base buffer's parser list and
parsers.  Now they can have their own parser list.

Useful; but I have long complained about the complex and inadequate treatment of multiple parsers in the same buffer. No, the range system is not good enough for complex cases as it depends on queries to work. This won’t help with that, but it’ll help with out-of-buffer rendering which is something.

New variable 'treesit-language-remap-alist'.
This variable allows a user to remap one language into another, such
that creating a parser for language A actually creates a parser for
language B.  By extension, any font-lock rules or indentation rules for
language A will be applied to language B instead.

This is useful for reusing font-lock rules and indentation rules of
language A for language B when language B is a strict superset of
language A.

New accessor functions for each setting in 'treesit-font-lock-settings'.
Now you can access a setting's query, feature, enable flag, and override
flag by 'treesit-font-lock-setting-query',
'treesit-font-lock-setting-feature', 'treesit-font-lock-setting-enable',
and 'treesit-font-lock-setting-override'.

New tree-sitter thing 'list'.
Unlike the existing thing 'sexp' that includes both lists and atoms,
'list' makes only lists be navigated by 'forward-sexp'.
The new command 'treesit-forward-sexp-list' uses 'list'
to move across lists.  But to move across atoms inside the list
it uses 'forward-sexp-default-function'.

New tree-sitter based functions for moving by lists.
If a major mode defines 'list' in 'treesit-thing-settings',
tree-sitter setup for these modes sets 'forward-list-function' to
'treesit-forward-list', 'up-list-function' to 'treesit-up-list', and
'down-list-function' to 'treesit-down-list'.  This enables the
'forward-list', 'up-list', and 'down-list' motion commands for those
modes.

New command 'treesit-cycle-sexp-thing'.
It cycles the type of navigation for commands that move across sexp's
and lists, such as 'treesit-forward-sexp', 'treesit-forward-list',
'treesit-down-list', and 'treesit-up-list'.  The type can be either
'list', the default, or 'sexp'.
With the default 'list' type, these commands move using syntax tables for
symbols and using the thing 'list' for lists.
With the 'sexp' type, these commands move across nodes defined by
the tree-sitter thing 'sexp' in 'treesit-thing-settings'.

So these changes are good in the sense that it is a marked improvement over the status quo before. Basically all the -sexp movement and editing commands were totally broken in TS-enabled modes because they had a really naive understanding of how -sexp commands work in basic Emacs that meant they didn’t do what you’d think they’d do in a tree-sitter-enabled major mode.

It’s not perfect (it never will be with a heuristic) but it’s better. See Combobulate: Structured Movement and Editing with Tree-Sitter for why.

Tree-sitter enabled modes now properly support 'show-paren-mode'.
They do that by letting 'show-paren-mode' use the results of parsing by
the tree-sitter library.  The new function 'treesit-show-paren-data' is
used to communicate the tree-sitter parsing results to 'show-paren-mode'.

Excellent.

Tree-sitter enabled modes now properly support 'hs-minor-mode'.
All commands from hideshow.el can selectively display blocks
defined by the new tree-sitter thing 'list'.

New tree-sitter thing 'comment'.
The new variable 'forward-comment-function' is set to the new function
'treesit-forward-comment' if a major mode defines the thing 'comment'.

New function 'treesit-query-eagerly-compiled-p'.
This function returns non-nil if a query was eagerly compiled.

New function 'treesit-query-source'.
This function returns the string or sexp source query of a compiled query.

New function 'treesit-language-display-name'.
This new function returns the display name of a language given the
language symbol.  For example, 'cpp' is translated to "C++".  A new
variable 'treesit-language-display-name-alist' holds the translations of
language symbols where that translation is not trivial.

New function 'treesit-merge-font-lock-feature-list'.
This function merges two tree-sitter font-lock feature lists.  It
returns a new font-lock feature list with no duplicates at the same
level.  It can be used to merge font-lock feature lists in a
multi-language major mode.

Another complaint of mine was that mode authors would hoard their tree-sitter font lock queries that you use to font lock a file. It means a major mode author can’t go “but I can have CSS and Ruby in this file” and then just pull the font lock queries from a variable from those major modes — it was not possible without introspecting a loaded buffer of each MM you wanted, which was… not great.

This merge feature does not solve that underlying problem but it does acknowledge at least that there are people out there building derivative modes that use multiple tree-sitter grammars. I mean, that’s the whole point of TS!

New function 'treesit-replace-font-lock-feature-settings'.
Given two tree-sitter font-lock settings, it replaces the feature in the
second font-lock settings with the same feature in the first font-lock
settings.  In a multi-language major mode it is sometimes necessary to
replace features from one of the major modes with others that are
better suited to the new multilingual context.

Yes, quite.

New variable 'treesit-aggregated-simple-imenu-settings'.
This variable allows major modes to setup Imenu for multiple languages.

New variable 'treesit-aggregated-outline-predicate'.
This variable allows major modes to setup 'outline-minor-mode'
for multiple languages.

New function 'treesit-simple-indent-add-rules'.
This new function makes it easier to customize indent rules for
tree-sitter modes.

I’m sure this is just wrapper around features already present in Stefan Monnier’s excellent SMIE (Simple-Minded Indentation Engine) that TS major modes typically use by default.

New function 'treesit-simple-indent-modify-rules'.
Given two tree-sitter indent rules, it replaces, adds, or prepends rules
in the old rules with new ones, then returns the modified rules.  In a
multi-language major mode it is sometimes necessary to modify rules from
one of the major modes to better suit the new multilingual context.

New variable 'treesit-simple-indent-override-rules'.
Users can customize this variable to add simple custom indentation rules
for tree-sitter major modes.

New variable 'treesit-languages-require-line-column-tracking'.
Now Emacs can optionally track line and column numbers for buffer edits
and send that information to tree-sitter parsers.  Parsers of languages
in this list will receive line and column information.  This is only
needed for very few languages.  So far only Haskell is known to need it.

New function 'treesit-tracking-line-column-p'.
New function to check if a buffer is tracking line and column for buffer
edits.

New function 'treesit-parser-tracking-line-column-p'.
New function to check if a parser is receiving line and column
information.

'treesit-language-at-point-function' is now optional.
Multi-language major modes can rely on the default return value from
'treesit-language-at' that uses the new function 'treesit-parsers-at'.

New function 'treesit-query-with-optional'.
When used in 'treesit-font-lock-rules', 'treesit-query-with-optional'
returns a default query plus the valid queries from a list of optional
queries.

New function 'treesit-query-with-fallback'.
When used in 'treesit-font-lock-rules', 'treesit-query-with-fallback'
selects the first valid query from a list.

Tree-sitter thing functions now work better with multiple parsers.
The following functions now better handle the case when there are
multiple parsers at point: 'treesit-thing-prev', 'treesit-thing-next',
'treesit-navigate-thing', 'treesit-thing-at'.  When there are multiple
parsers at point, instead of using whatever 'treesit-node-at' returns at
point, these functions now try every relevant parser in descending order
of relevance.  (Deeper-embedded parsers have higher relevance.)  These
functions now also take an additional optional argument, PARSER, that
allows the caller to specify a parser or language to use.  That also
means 'treesit-beginning/end-of-defun' can now move across parsers.

Good. Multi-language parsing in a buffer is still not great but we’re slowly getting there.

New command 'treesit-explore'.
This command replaces 'treesit-explore-mode'.  It turns on
'treesit-explore-mode' if it is not on, and pops up the explorer buffer
if it is already on.

'treesit-explore-mode' now supports local parsers.
Now 'treesit-explore-mode' (or 'treesit-explore') prompts for a parser
rather than a language, and it is now possible to select a local parser
at point to explore.

I could never get these things to behave properly. They’d leave weird minor mode detritus in the calling buffer; stick around and get reactivated when a desktop file is read on startup. I’m hoping that is fixed also.

Tree-sitter query predicates ':equal', ':match', and ':pred' are deprecated.
Use ':eq?', ':match?', and ':pred?' instead.  The change is because
newer tree-sitter libraries mandate query predicates to end with a
question mark.  Emacs will transparently convert ':equal', ':match', and
':pred' to ':eq?', ':match?', and ':pred?', respectively, so existing
queries still work fine with the latest tree-sitter library.  The
predicate ':equal' is changed to ':eq?' to better follow tree-sitter's
convention.  Also, the ':match?' predicate can now take the regexp as
either the first or second argument, so it works with both tree-sitter
convention (regexp arg second) and Emacs convention (regexp arg first).

I don’t understand why this change couldn’t have been handled purely in the backend. It is not possible to talk to the actual tree-sitter library itself; it’s gated behind treesit.el and Emacs core. I do not understand why the backend couldn’t just rewrite these query matchers and just leave it at that. Why deprecate?

Track changes

New variable 'track-changes-undo-only' to distinguish undo changes.

Hideshow

Hideshow is Emacs’s code/structured text hiding system.

New command 'hs-cycle'.
This command cycles the visibility state of the current block between
hiding the parent block, hiding only the nested blocks and showing all
the blocks.

New user option 'hs-cycle-filter' for visibility-cycling with 'TAB'.
This user option controls the positions on the headline of hideable blocks
where the 'TAB' key cycles the blocks' visibility.

New command 'hs-toggle-all'.
This command hides or shows all the blocks in the current buffer.

'hs-hide-level' no longer hides all the blocks in the current buffer.
If 'hs-hide-level' was not inside a code block, it would hide all the
blocks in the buffer like 'hs-hide-all'.  Now it only hides all the
second level blocks.

New user option 'hs-display-lines-hidden'.
If this option is non-nil, Hideshow displays the number of hidden lines
next to the ellipsis.  By default this is disabled.

New user option 'hs-show-indicators'.
This user option determines if Hideshow should display indicators to
show and toggle the block hiding.  If non-nil, the indicators are enabled.
By default this is disabled.

New user option 'hs-indicator-maximum-buffer-size'.
This user option limits the display of Hideshow indicators to buffers
that are not too large.  By default, buffers larger than 2MB have the
indicators disabled; a value of nil will activate the indicators
regardless of the buffer size.

New user option 'hs-indicator-type'.
This user option determines which indicator type should be used for the
block indicators.

The possible values are: 'fringe' to display the indicators in the
fringe (the default); 'margin' to display the indicators in the margin;
and nil, to display the indicators at end-of-line.

The new icons 'hs-indicator-show' and 'hs-indicator-hide' can be used to
customize the indicators appearance, but apply only if
'hs-indicator-type' is set to 'margin' or nil.

The hiding behavior of some hideshow commands has changed.
'hs-hide-block', 'hs-hide-level', 'hs-cycle' and 'hs-toggle-hiding' now
hide the innermost block to which the current line belongs instead of
the block after point.  To restore the old behavior, set the new user
option 'hs-hide-block-behavior' to 'after-point'.

The variable 'hs-special-modes-alist' is now obsolete.
Instead of customizing Hideshow for a mode by setting the elements of
'hs-special-modes-alist', such as START, COMMENT-START,
FORWARD-SEXP-FUNC, etc., major mode authors should set the corresponding
buffer-local variables 'hs-block-start-regexp', 'hs-c-start-regexp',
'hs-forward-sexp-function', etc.

'hs-hide-level' can now hide comments too.
This is controlled by 'hs-hide-comments-when-hiding-all'.

New minor mode 'hs-indentation-mode'.
This buffer-local minor mode configures 'hs-indentation-mode' to detect
blocks based on indentation.

The new user option 'hs-indentation-respect-end-block' can be used to
adjust the hiding range for this minor mode.

That is truly useful. Particularly for YAML.

C-ts mode

This and any future mode with -ts in it, is specifically for the tree-sitter-flavored version of a major mode. Do note that with few exceptions, the TS major modes are usually far less feature rich than the major modes they try to replace.

New user option 'c-ts-mode-enable-doxygen'.
By default, this is nil, and the Doxygen comment blocks in C/C++ sources
are highlighted like other comments.  When non-nil, Doxygen comment
blocks are font locked if the Doxygen grammar library is available.

Csharp-ts mode

Renamed feature in 'treesit-font-lock-feature-list'.
The feature 'property' has been renamed to 'attribute', since this is
what it is generally called among C# programmers.

Go-ts mode

New unit test commands.
Three new commands are now available to run unit tests.

The 'go-ts-mode-test-function-at-point' command runs the unit test at
point.  If a region is active, it runs all the unit tests under the
region.  It is bound to 'C-c C-t t' in 'go-ts-mode'.

The 'go-ts-mode-test-this-file' command runs all unit tests in the current
file.  It is bound to 'C-c C-t f' in 'go-ts-mode'.

The 'go-ts-mode-test-this-package' command runs all unit tests under the
package of the current buffer.  It is bound to 'C-c C-t p' in 'go-ts-mode'.

The 'go-ts-mode-build-tags' user option is available to set a list of
build tags for the test commands.

The 'go-ts-mode-test-flags' user option is available to set a list of
additional flags to pass to the go test command line.

Lua-ts mode

New user option 'lua-ts-auto-close-block-comments'.
When non-nil, inserting a block comment "--[[" will close it by
inserting its respective "]]".  By default, this is disabled.

Java-ts mode

New user option 'java-ts-mode-enable-doxygen'.
By default, this is nil, and the Doxygen comment blocks in Java sources
are highlighted like other comments.  When non-nil, Doxygen comment
blocks are font locked if the Doxygen grammar library is available.

New user option 'java-ts-method-chaining-indent-offset'.
Now method chaining is indented by 8 spaces rather than 4, and this
option controls how much is indented for method chaining.

JSON-ts mode

New command 'json-ts-jq-path-at-point'.
This command copies the path of the JSON element at point to the
kill-ring, but formatted for use with the 'jq' utility.

Now that is handy. One of the actual benefits of tree-sitter’s concrete syntax tree.

PHP-ts mode

'php-ts-mode' now depends on 'mhtml-ts-mode'.
The direct dependency on 'js-ts-mode', 'css-ts-mode' and 'html-ts-mode'
has now been replaced by 'mhtml-ts-mode'.  Navigation, Outline and Imenu
work for all languages, and code maintenance is easier.

'php-ts-mode-run-php-webserver' can now accept a custom "php.ini" file.
You can use the new optional argument CONFIG when calling
'php-ts-mode-run-php-webserver' to pass an alternative "php.ini" file to
the built-in Web server.  Interactively, when invoked with a prefix
argument, 'php-ts-mode-run-php-webserver' prompts for the config file as
well as for other connection parameters.

The user option 'php-ts-mode-css-fontify-colors' has been removed.
'mhtml-ts-mode-css-fontify-colors' replaces this option.

New user option 'php-ts-mode-html-relative-indent'.
In buffers containing both PHP and HTML, this option allows you to
define how the PHP code should be indented relative to the position of
the HTML tags.

New user option 'php-ts-mode-html-indent-offset'.
Offset of PHP code block relative to HTML tags.

New user option 'php-ts-mode-find-sibling-rules'.
Rules for finding siblings of a PHP file.

New user option 'php-ts-mode-phpdoc-highlight-errors'.
When non-nil, it highlights unknown PHPDOC tags using
'font-lock-warning-face' so that the user can identify them more easily.

New command 'php-ts-mode-show-ini'.
Show the location of the PHP ini files.  If the current buffer is
associated to a remote PHP file, show the remote PHP ini files.

Rust-ts mode

New user option 'rust-ts-mode-fontify-number-suffix-as-type'.
Rust number literals may have an optional type suffix.  When this option
is non-nil, this suffix is fontified using 'font-lock-type-face'.

YAML-ts mode

New user option 'yaml-ts-mode-yamllint-options'.
Additional options for 'yamllint', the command used for Flymake's YAML
support.

EIEIO

EIEIO is Emacs’s CLOS-style Object-Oriented Programming system. Named after the nursery rhyme “Old McDonald had a farm… EIEIO”.

Good ole’ Ludlam who wrote it had a thing for farm-related naming. See also his “Semantic Bovinator”, a tree-sitter precursor from the 2000s.

New value 'warn' for 'eieio-backward-compatibility'.
This is the new default value and causes warnings to be emitted
at run-time for the use of the associated deprecated features.
'(setq eieio-backward-compatibility t)' can be used to recover
the previous silence.

Text mode

New commands to convert between ASCII and full-width characters.
New commands 'fullwidth-region' and 'fullwidth-word' convert ASCII
characters in region or in the word at point to the corresponding
full-width characters, which are customarily used instead of ASCII
characters in CJK texts.  For example, 'A' is converted to 'Ａ', '1' is
converted to '１', etc.  Companion commands 'halfwidth-region' and
'halfwidth-word' perform the opposite conversion.

Texinfo mode

Texinfo mode now can auto-close the ``'' pairs.
Now inserting `` in 'texinfo-mode' will close it by inserting its
respective '', if 'electric-pair-mode' is enabled.

ASM mode

'asm-mode-set-comment-hook' is obsolete.
You can now set 'asm-comment-char' from 'asm-mode-hook' instead.

Ibuffer

IBuffer is a fantastic and superior buffer list manager in Emacs. Do try it out and look around online for cool configs for it.

New column 'recency' in Ibuffer display.
The user option 'ibuffer-formats' configures the Ibuffer formats.  Add
'recency' to the format to display the column.

New value 'title' for the user option 'ibuffer-use-header-line'.
Display column titles in the header line if 'ibuffer-use-header-line' is
set to 'title'.

New user option 'ibuffer-human-readable-size'.
When non-nil, buffer sizes are shown in human readable format.

'define-ibuffer-op' prompts can now be functions.
The prompts 'opstring' and 'active-opstring' can now either be strings
or functions.  This is useful when your prompts can benefit from dynamic
content.

New Ibuffer-dedicated faces.
New faces 'ibuffer-marked', 'ibuffer-deletion', 'ibuffer-title', and
'ibuffer-filter-group-name'.  By default, they inherit from the
general-purpose faces Ibuffer previously used, to preserve previous
behavior.

ElDoc

Eldoc is Emacs’s interactive, point-driven documentation and code lookup tool. See Seamlessly Merge Multiple Documentation Sources with Eldoc for more information.

New ElDoc function 'elisp-eldoc-funcall-with-docstring'.
This function includes the current function's docstring in the ElDoc
echo area and can be used as a more detailed alternative to
'elisp-eldoc-funcall'.

New user option 'elisp-eldoc-funcall-with-docstring-length'.
This user option specifies how long function docstrings must be
displayed in 'elisp-eldoc-funcall-with-docstring'.  If set to 'short'
(the default), only display the first sentence of the docstring.
Otherwise, if set to 'full', display the full docstring.

New user option 'elisp-eldoc-docstring-length-limit'.
This user option controls the maximum length of docstrings in character
units that 'elisp-eldoc-funcall-with-docstring' and
'elisp-eldoc-var-docstring-with-value' will show.  By default, it is set
to 1000 characters.

Buffer Menu

The default buffer list manager bound to C-x C-b. Replace it with M-x ibuffer.

New user option 'Buffer-menu-human-readable-sizes'.
When non-nil, buffer sizes are shown in human readable format.  The
default is nil, which retains the old format.

Term

Emacs’s terminal emulator. See Running Shells and Terminal Emulators in Emacs

The terminal emulator now supports auto-margins control.
Term mode now handles DECAWM escape sequences that control whether text
automatically wraps at the right margin:

- \e[?7h enables auto-margins (default)
- \e[?7l disables auto-margins

When auto-margins is disabled, characters that would go beyond the right
margin are discarded, which matches the behavior of physical terminals
and other terminal emulators.  Control sequences and escape sequences
are still processed correctly regardless of margin position.

SMerge mode

SMerge is one of several conflicting (pardon the pun) ways of handling merge conflicts in Emacs. I like it.

New 'repeat-map' for SMerge conflict resolution commands.
With 'repeat-mode' enabled, after invoking an SMerge command (for
example, 'C-c ^ n'), you can repeat further SMerge commands by typing
just the final key (for example, 'n', 'p', 'u', 'l').

Oh gosh yes. I love SMerge but C-c ^ n (and friends) is exactly why people who are not Emacs users bounce hard when they see a key binding like that.

New command 'smerge-extend' extends a conflict over surrounding lines.

New command 'smerge-refine-exchange-point' to jump to the other side.
When used inside a refined chunk, it jumps to the matching position in
the other side of the refinement: if you are in the new text, it jumps
to the corresponding position in the old text and vice versa.

New user option 'smerge-refine-shadow-cursor'.
When 'smerge-refine' shows the conflict diffs at word granularity, a
shadow cursor is now displayed in the lower version when point is in the
upper version, and vice versa.  The shadow cursor is just the character
corresponding to the position where 'smerge-refine-exchange-point' would
jump, shown in a new distinct face 'smerge-refine-shadow-cursor', by
default a box face.

'smerge-refine-regions' can compare regions in different buffers.

Cursor Sensor mode

Now here’s an obscure mode. It and the intangible cursor concept are basically just a way of taking clumps of characters and telling Emacs that it should, and I’m keeping it a bit simple here, treat them as one big cohesive unit for all intents. I have only ever used an intangible cursor property once and that was in Combobulate’s envelope system.

New direction 'moved' used when the cursor moved within the active area.

Image Dired

Yep, Emacs’s dired has a thumbnail image viewer system.

'image-dired-show-all-from-dir' takes the same first argument as 'dired'.
This allows passing a string with wildcards, or a cons cell where the
first element is a list and the rest is a list of files.

New single-letter bindings in 'image-dired-thumbnail-mode-map'.
The keys 'f', 'b', 'n', 'p', 'a' and 'e' are now bound to the same
commands as their 'C-' counterparts.

Browse URL

Browse URL is just a wide-ranging set of internal functions, user-facing commands and variables that govern how Emacs pass URL-related information in and out; stuff like opening a browser when you click an url.

New user option 'browse-url-transform-alist'.
This user option is an alist that allows transforming URLs before asking
a web browser to load them.  For example, it could be used like this:

    (add-to-list 'browse-url-transform-alist
                 '("vim\\.org/.*" . "gnu.org/software/emacs/"))

New command 'browse-url-qutebrowser' for Qutebrowser.
For better integration with Qutebrowser, set
'browse-url(-secondary)-browser-function' to 'browse-url-qutebrowser'.

New GTK-native launch mode.
For better Wayland support, the pgtk toolkit exposes a new
'x-gtk-launch-uri' browse-url handler and uses it by default when URLs
are browsed from a PGTK frame.  For other frames, we fall back to the
default URL launch function.  This change allows us to properly raise
browser windows under Wayland using the xdg_activation_v1 protocol.

'RET' can visit URLs in read-only buffers.
In some keymaps such as 'ansi-osc-hyperlink-map',
'browse-url-button-map', 'goto-address-highlight-keymap', and
'bug-reference-map', it is now possible to visit URLs by typing just
'RET' instead of 'C-c RET' in read-only buffers.

Removed support for some obsolete web browsers.
Conkeror (obsolete since Emacs 28.1), gnome-moz-remote (obsolete since
Emacs 25.1), and gnudoit (obsolete since Emacs 25.1).

'browse-url-firefox-program' now supports LibreWolf and Zen Browser.
LibreWolf, Floorp and Zen Browser, three popular Firefox forks, have been
added to the programs that are automatically recognizable as Firefox
workalikes.  Emacs will set 'browse-url-firefox-program' to the first
one of these found on your system.

Floorp?

CL-Lib

Derived types (i.e. 'cl-deftype') can now be used as method specializers.

Some cl-lib functions and macros are now built-in.
These functions or macros have been added to Emacs Lisp, and the old
names are now aliases for the built-in equivalents:

- 'cl-incf'      renamed to 'incf'
- 'cl-decf'      renamed to 'decf'
- 'cl-oddp'      renamed to 'oddp'
- 'cl-evenp'     renamed to 'evenp'
- 'cl-plusp'     renamed to 'plusp'
- 'cl-minusp'    renamed to 'minusp'
- 'cl-member-if' renamed to 'member-if'

'cl-member-if' is marked obsolete.  The other names are deprecated too,
and will be marked as obsolete in a future release.

Common Lisp idioms continue advancing from the rear echelons into Emacs proper, much to the chagrin of some people.

'cl-labels' now also accepts '(FUNC EXP)' bindings, like 'cl-flet'.
Such bindings make it possible to compute the function to bind to FUNC.

'cl-block' names are now lexically scoped, as documented.

'cl-locally' is now obsolete.
It is an alias for the 'progn' special-form.

'cl-declare' is now obsolete; use 'defvar' instead.

'cl-gensym' is now obsolete; use 'gensym' instead.

New macro 'cl-with-accessors'.
This macro is similar to 'with-slots', but uses accessor functions
instead of slot names.  It is useful when some slot accessor functions
are used repeatedly, such as reading from a slot and then writing to
that slot.  Symbol macros are created for the accessor functions using
'cl-symbol-macrolet', so they can be used with 'setq' and 'setf'.

Unless I am mistaken, with-slots can already use setf to set a slot? I must be reading the text wrong.

Whitespace

Don’t sleep on M-x whitespace-mode and friends for finding errant whitespaces, tabs, and so forth. You won’t need it often, but when you do…

'whitespace-cleanup' now adds a missing newline at end of file.
If 'whitespace-style' includes 'missing-newline-at-eof' (which is the
default), the 'whitespace-cleanup' function will now add the newline.

'whitespace-mode' can now prettify page delimiter characters ('^L').
If 'page-delimiters' is set in 'whitespace-style', or the new minor mode
'whitespace-page-delimiters-mode' is on, the page delimiter character
('^L') is displayed as a pretty horizontal line that spans the entire
width of the window.  The new 'whitespace-page-delimiter' face can be
used to customize the appearance.

New user option 'whitespace-global-mode-buffers'.
Normally, 'global-whitespace-mode' skips special buffers whose name
starts with an asterisk "*".  This user option provides an override: it
contains a list of regular expressions used to match the names of
special buffers in which 'global-whitespace-mode' should turn on.  The
default value preserves the existing exception for the "*scratch*"
buffer.

Bookmark

One of Emacs’s greatest features. The bookmark system. You can bookmark a wide range of things and Emacs will happily pop open that exact spot in the info manual you bookmarked. Low-key fantastic feature.

Bookmark history now saves each bookmark only once.
Previously, the variable 'bookmark-history' accumulated duplicate
bookmark names when bookmark features were used interactively.  This
made their history larger than necessary for frequent bookmark users.
Bookmark names are now saved uniquely.

New user option 'bookmark-bmenu-type-column-width'.
This user option controls the width of the type column on the bookmark
menu 'bookmark-bmenu-list'.  The default value is 8 which is backwards
compatible.

New hook 'bookmark-after-load-file-hook'.
This hook is run by 'bookmark-load' after loading a bookmark file.  This
hook can be used, for example, to reconcile 'bookmark-alist' against
bookmark state that you, or a package that you use, maintains.

Recentf

A store of recent files. Back in the day it was a bit of a pain to use due to the way completion mechanism worked, so I wrote Find files faster with the recent files package. Nowadays your fancy completion package + M-x recentf is all you need

You can now regularly auto-save recently opened files.
Customize user option 'recentf-autosave-interval' to the number of
seconds between auto saving recently opened files.  For example,
customize this variable to 300 to save recently opened files every 5
minutes.  From Lisp, use 'setopt', not 'setq'.  If
'recentf-autosave-interval' is nil, auto saving is disabled; this is the
default.

New user option 'recentf-show-messages'.
'recentf-save-list' can print a message when saving the recentf list.
The new option, if customized to nil, suppresses this message.

New user option 'recentf-suppress-open-file-help'.
By default, invoking 'recentf-open-files' displays a message saying what
action clicking or typing 'RET' on the item at point executes, and tabbing
between items in the "*Open Recent*" buffer likewise displays such
messages.  To suppress these messages, customize the user option
'recentf-suppress-open-file-help' to non-nil.  The default value of this
option is nil.

New user option 'recentf-exclude-ignored-extensions'.
Add the new predicate function 'recentf-exclude-file-by-extension-p' to
the list that is the value of the user option 'recentf-exclude' to
ignore files with certain extensions.  By default, adding this function
to 'recentf-exclude' ignores files whose extensions are listed in
'completion-ignored-extensions'; you can specify a different list of
extensions by customizing the new user option
'recentf-exclude-ignored-extensions'.

Saveplace

M-x save-place-mode stores the exact place you were in a file when you revisit it.

You can now regularly auto-save places.
Customize user option 'save-place-autosave-interval' to the number of
seconds between auto-saving places.  For example, customize this
variable to 300 to save places every 5 minutes.  From Lisp, use 'setopt',
not 'setq'.  If 'save-place-autosave-interval' is nil, auto saving is
disabled; this is the default.

Savehist

Tired of losing history in all manner of completion prompts? Enable M-x savehist-mode and you can choose what and where is saved.

The history file can be modified by external tools.
Emacs can now handle this case gracefully by merging the external and
internal history information.  This feature is activated only when
'savehist-additional-variables' is nil.

Savehist no longer saves additional variables more than once.
If you configured 'savehist-additional-variables' with variables that
were also dynamically accumulated in minibuffer history during
minibuffer use, they are now saved only once in the file specified by
'savehist-file'.  Previously, they were saved twice.

Rectangle Mark

Borrowed from CUA-mode that for some reason got special rectangle selection but the rest of us non-CUA users did not. It was moved out some years ago and nowC-x SPC activates it.

New user option to control whether empty rectangle selections are shown.
The new user option 'rectangle-indicate-zero-width-rectangle' can be
used to disable the default display of empty rectangular selections.
The default is t; set it to nil to disable the indication.  (It causes a
horizontal shift of text on display, which could be distracting.)

Message

One of several ways of crafting RFC-compliant e-mails in Emacs.

"In-Reply-To" header contains only a message id.
The "In-Reply-To" header created when replying to a message now contains
only the originating message's id, conforming to RFC 5322.  The previous
behavior included additional information about the originating message.
The new user option 'message-header-use-obsolete-in-reply-to', nil by
default, can be set to a non-nil value to restore the previous behavior.

Or should I say: compliant now?

'message-subject-re-regexp' default value is derived from 'mail-re-regexps'.
'mail-re-regexps' is a new user option that is easier to customize than
'message-subject-re-regexp'.  'message-subject-re-regexp' is still
honored if it was already set.

'message-strip-subject-re' now matches case-insensitively.

'message-change-subject' inserts the current subject into future history.

Hashcash support has been removed.
It is believed to no longer be useful as a method to fight spam.  The
'message-generate-hashcash' option is now obsolete and has no effect.

Gnus

A one-man marching band that started its life as a usenet group reader. Incredibly complex and feature rich reader that, after decades of being brow-beaten with a rolled-up newspaper, can now also handle your emails, reddit chats, rss feeds and probably a lot more than that.

Replying to icalendar events now supports specifying a comment.
When called with a prefix argument, accepting, declining, or tentatively
accepting an icalendar event will prompt for a comment to add to the
response.

Hashcash support has been removed.
It is believed to no longer be useful as a method to fight spam.  The
'spam-use-hashcash' hook is now obsolete and has no effect.

Add 'M-i' keybinding as the symbolic prefix in the group keymap.
The symbolic prefix is another kind of universal prefix that is used in
Gnus; see "(gnus) Symbolic Prefixes" in the Gnus manual.

Sorting selected groups is now possible with 'gnus-topic-mode'.

gnus-dbus.el is now obsolete.

System sleep integration is now independent of D-Bus.
The system sleep integration previously provided by customizing the
variable 'gnus-dbus-close-on-sleep' is now deprecated.  A new system
using the builtin system-sleep.el library is now available by customizing
'gnus-close-on-sleep'.  This will work on all systems that the
'system-sleep' library supports.

Sieve

Major mode for server-side IMAP sieve filters.

New keybinding to refresh buffer in 'sieve-manage-mode'.
'sieve-refresh-scriptlist' is now bound to 'g' to refresh the contents
of the current sieve buffer.

Button

Emacs’s widget system (what customize uses) is used here to turn stuff like #29382 bug reference notations into little interactive buttons.

If you like this paradigm, just use Bob Weiner’s Hyperbole package. It’s far better.

New function 'unbuttonize-region'.
It removes all the buttons in the specified region.

Disabling 'button-mode' now removes all buttons in the current buffer.

Shell

My favorite method of interacting with shells. Nothing more than a riced Emacs buffer serving up cooked terminal output. See Running Shells and Terminal Emulators in Emacs

Shell buffers now support bookmarks.
You can now bookmark local and remote shell buffers using the bookmark
menu 'bookmark-bmenu-list', or by using the command 'bookmark-set'.
Shell bookmarks can be loaded via the menu and by using the command
'bookmark-jump', which opens a bookmarked shell, restores its buffer name,
its current directory, and creates a remote connection, if necessary.
You can customize 'shell-bookmark-name-function'.

Bookmarks are awesome. I’ll have to play with this for sure

New command to complete the shell history.
'comint-complete-input-ring' ('C-x <UP>') is like 'minibuffer-complete-history'
but completes on comint inputs.

See my Shell & Comint Secrets: History commands

'ansi-osc-directory-tracker' now respects remote directories.
Remote directories are now retained when changes to 'default-directory'
are detected by this filter.  For example, "/ssh:hostname:/home/username"
would have been stripped to just "/home/username" before.

OSC directory tracking is especially important in shell mode for it does not typically ask the underlying shell for “completion”.

Eshell

Emacs’s very own shell written in Elisp. Cool package. See Mastering Eshell.

New interactive command 'eshell-clear'.
This command scrolls the screen so that only the current prompt is
visible, optionally erasing all the previous input/output as well.
Previously, the Eshell built-in command 'eshell/clear' supported this
(e.g., to call it via 'M-x'), but this new command behaves more
consistently if you have a partially typed command at the Eshell prompt.

New user option 'eshell-command-async-buffer'.
This option lets you tell 'eshell-command' how to respond if its output
buffer is already in use by another invocation of 'eshell-command', much
like 'async-shell-command-buffer' does for 'shell-command'.  By default,
this will prompt for confirmation before creating a new buffer when
necessary.  To restore the previous behavior, customize this option to
'confirm-kill-process'.

'eshell-execute-file' is now an interactive command.
Interactively, this now prompts for a script file to execute.  With the
prefix argument, it will also insert any output into the current buffer
at point.

'eshell-command' and 'eshell-execute-file' can now say where stderr goes.
These functions now take an optional ERROR-TARGET argument to control
where to send the standard error output.
See the Info node "(eshell) Entry Points" for more details.

You can now loop over ranges of integers with the Eshell 'for' command.
When passing a range like 'BEGIN..END' to the Eshell 'for' command,
Eshell will now iterate over each integer between BEGIN and END, not
including END.

Conditional statements in Eshell now use an 'else' keyword.
Eshell now prefers the following form when writing conditionals:

    if {conditional} {true-subcommand} else {false-subcommand}

The old form (without the 'else' keyword) is retained for compatibility.

You can now chain conditional statements in Eshell.
When using the newly-preferred conditional form in Eshell, you can now
chain together multiple 'if'/'else' statements.  For more information,
see "(eshell) Control Flow" in the Eshell manual.

Eshell's built-in 'wait' command now accepts a timeout.
By passing '-t' or '--timeout', you can specify a maximum time to wait
for the processes to exit.  Additionally, you can now wait for external
processes by passing their PIDs.

New hook 'eshell-after-initialize-hook'.
This hook runs after an Eshell session has been fully initialized,
immediately before running 'eshell-post-command-hook' for the first
time.

Improved history Isearch.
History Isearch in Eshell has been reworked.  Two new commands
'eshell-isearch-backward-regexp' and 'eshell-isearch-forward-regexp' are
added for incrementally searching through the input history.
'eshell-isearch-backward-regexp' is bound to 'M-r' by default, and 'M-s'
is freed for normal search commands.  If you would like to restore the
previous key-bindings for the non-incremental search commands, put in
your configuration:

    (with-eval-after-load 'em-hist
      (keymap-set eshell-hist-mode-map "M-r"
                  #'eshell-previous-matching-input)
      (keymap-set eshell-hist-mode-map "M-s"
                  #'eshell-next-matching-input))

Eshell was sorely missing the interactive reverse search

New user option 'eshell-history-isearch'.
When 'eshell-history-isearch' is nil (the default), Isearch commands
search in the buffer contents.  If you customize it to t, those commands
only search in input history.  If you customize it to the symbol 'dwim',
those commands search in input history only when point is after the last
prompt.

Eshell 'alias' command now sorts the alias list.
When adding an alias interactively, Eshell now sorts the list of aliases
before saving the alias file.  This maintains the stability of the
list of aliases to make the diff between versions more readable if you
store your aliases in version control.

I’m happy somebody’s taken ownership of eshell and is busy adding cool new features.

Mail Utils

New user option 'mail-re-regexps'.
This contains the list of regular expressions used to match "Re:" and
international variants of it when modifying the Subject field in
replies.

Mairix

Mairix is apparently a mail search engine. I have never used it.

'mairix-search' now keeps its own minibuffer history.

Imap

'imap-authenticate' can now use PLAIN authentication.
"AUTH=PLAIN" support is auto-enabled if the IMAP server supports it.  If
you do not wish to use "AUTH=PLAIN", pass a specific authentication type
to 'imap-open' for 'imap-authenticate' to use, or remove 'plain' from
'imap-authenticators'.

Rmail

Another way to author your emails in Emacs. So that’s 3 so far: Message, Gnus and Rmail.

'rmail-re-abbrevs' default value is now derived from 'mail-re-regexps'.
'mail-re-regexps' is a new user option that is easier to customize than
'rmail-re-abbrevs'.  'rmail-re-abbrevs' is still honored if it was
already set.

New user options for formatting Rmail summary lines.
'rmail-summary-sender-function' and 'rmail-summary-recipient-function'
control how the sender/recipient fields are displayed in the summary.
'rmail-summary-address-width' controls the width of that field.

New user option 'rmail-mime-save-action'.
This option specifies an action to take after saving a MIME attachment.
Predefined values include visiting the file in Emacs, jumping to the
file in Dired, or opening the file with an external program.  You can
also provide a custom function.

Rmail now detects email messages from suspicious sender addresses.
If the "From" header of a message contains a suspicious email address,
Rmail will now highlight it in a distinct face and provide a 'help-echo'
tooltip explaining the reason.  (What exactly is considered as
suspicious email addresses is determined by the function
'textsec-suspicious-p', which see.)  This is controlled by the new user
option 'rmail-detect-suspicious-headers', whose default value is
non-nil; customize to nil to disable the check.

Sendmail

Sending an email via sendmail.el checks for suspicious addressees.
The command 'mail-send', used to send email in Mail mode, now checks the
addressees for suspicious email addresses.  If such addresses are found,
the command will show them and the reason they are considered
suspicious, and will request a confirmation before sending the message.
This follows the behavior of Message mode, and affects users who
customize 'mail-user-agent' to the value 'sendmail-user-agent'.

SHR

SHR is Emacs’s internal HTML rendering engine. It powers M-x eww, Emacs’s Web Wowser.

SHR now slices large images into rows.
Sliced images allow for more intuitive scrolling up/down by letting you
scroll past each slice, instead of jumping past the entire image.
Previously, SHR sliced images when zoomed to their original size, no
matter how large or small that was.  Now, SHR slices any images taller
than 'shr-sliced-image-height'.  For more information, see the Info node
"(eww) Advanced".

You can now customize the image zoom levels to cycle through.
By customizing 'shr-image-zoom-levels', you can change the list of zoom
levels that SHR cycles through when calling 'shr-zoom-image'.

New user option 'shr-fill-text'.
When 'shr-fill-text' is non-nil (the default), SHR will fill text
according to the width of the window.  If you customize it to nil, SHR
will leave the text as-is; in that case, EWW will automatically enable
'visual-line-mode' when displaying a page so that long lines are
visually wrapped at word boundaries.

EWW

Emacs’s Web Wowser. M-x eww. Handy little text and image browser; great for documentation.

EWW now enables 'visual-wrap-prefix-mode' when 'shr-fill-text' is nil.
By default, 'shr-fill-text' is t, and EWW fills the text according to
the width of the window.  If you customize 'shr-fill-text' to nil, EWW
will now automatically turn on 'visual-wrap-prefix-mode' in addition to
'visual-line-mode', so that long lines are wrapped at word boundaries
near the window edge, and continuation lines are indented using prefixes
computed from the surrounding context.

New user option 'eww-guess-content-type-functions'.
The value is a list of functions that EWW should call to determine the
content-type of Web pages which don't have a valid 'Content-Type'
header.  The default value is a function that considers a page with an
HTML 'doctype' declaration to have content-type "text/html".

'eww-switch-to-buffer' falls back to calling 'eww'.
When there is no EWW buffer, 'eww-switch-to-buffer' falls back to
calling 'eww'.

URL Queue

One of several ways of querying a HTTP endpoint.

'url-queue-retrieve' now makes use of some url request variables.
The variables 'url-request-data', 'url-request-method', and
'url-request-extra-headers' can now be bound around a call to
'url-queue-retrieve'.  Binding them has the same effect as for
'url-retrieve'.

CC mode

Classic C mode.

New type of 'c-offsets-alist' element.
The 'cdr' of such an alist element may now be a syntactic symbol.  A
source line with a syntactic element whose symbol is the 'car' of that
alist element is indented as though it were the 'cdr'.

Enums now have their own syntactic symbols.
The new symbols 'enum-open', 'enum-close', 'enum-intro' and
'enum-entry' are used in the analysis of enum constructs.  Previously,
they were given 'brace-list-open', etc.  These are fully described in
the "(ccmode) Enum Symbols" node of the CC mode manual.

Enums are now, by default, indented like classes, not brace-lists.
To get the old behavior back, add an element '(enum-open
. brace-list-open)' to 'c-offsets-alist' in your CC mode style, or amend
'c-offsets-alist' likewise in any of the other ways detailed in the
"(ccmode) Config Basics" node of the CC mode manual.

Emacs Lisp mode

Semantic highlighting support for Emacs Lisp.
'emacs-lisp-mode' can now use code analysis to highlight more symbols
more accurately.  Customize the new user option
'elisp-fontify-semantically' to non-nil to enable this feature, and see
the Info node "(emacs) Semantic Font Lock" for more information.

Awesome. Can’t wait to try it out.

Checkdoc will now flag incorrect formatting in warnings.
This affects calls to 'warn', 'lwarn', 'display-warning', and
'message-box'.

New function 'checkdoc-batch'.
It checks the buffer in batch mode, prints all found errors
and signals the first found error.

New file-local variable 'lisp-indent-local-overrides'.
This variable can be used to locally override the indent specification
of symbols.

Checkdoc no longer warns about missing footer lines in some cases.
Emacs Lisp libraries have traditionally ended with a footer line
(sometimes referred to as "terminating comment").  Their purpose was to
easily detect files that had been truncated in transit on ancient and
less reliable connections:

    ;; some-cool-package.el ends here

'checkdoc' will no longer warn if that line is missing for packages that
explicitly only support Emacs 30.1 or later, as specified in the
"Package-Requires" header.  The reason for keeping the warning for
packages that support earlier versions of Emacs is that package.el in
those versions can't install packages where that line is missing.

This change affects both 'checkdoc' and the corresponding flymake
backend.

Checkdoc no longer warns about wide docstrings.
The Checkdoc warning for wide docstrings duplicates the byte-compiler
warning added in Emacs 28.1.  This redundancy is now removed.

New user option 'checkdoc-arguments-missing-flag'.
Set this to nil to disable warnings for function arguments that are not
documented in docstrings.

New user option 'checkdoc-allow-quoting-nil-and-t'.
Customizing this option to a non-nil value stops checkdoc from warning
for docstrings where symbols 'nil' and 't' are in quotes.

The default of 'checkdoc-verb-check-experimental-flag' is now nil.
In most cases, having it enabled leads to a large amount of false
positives.

IELM

IELM is the Interactive Emacs Lisp Mode. A REPL for Elisp. See Evaluating Elisp in Emacs.

IELM input history is now saved also when the IELM process is killed.
When you kill the IELM process with 'C-c C-c', the input history is now
saved to the file specified by 'ielm-history-file-name', just like when
you exit the Emacs session or kill the IELM buffer.

New value 'point' for user option 'ielm-dynamic-return'.
When 'ielm-dynamic-return' is set to 'point', typing 'RET' has dynamic
behavior based on whether point is inside an sexp.  While point is
inside an sexp typing 'RET' inserts a newline, and otherwise Emacs
proceeds with evaluating the expression.  This is useful when
'electric-pair-mode', or a similar automatic pairing mode, is enabled.

Very handy as the multi-line editing behavior in IELM is a little bit wonky. Honestly IELM is a terrible choice if you’re doing multi-line stuff; use a scratch buffer or better still an ert test.

Doc View

Doc View turns complex documents like PDF and MS word into images so Emacs can render and show them to you.

Dedicated buffer for plain text contents.
When switching to the plain text contents with 'doc-view-open-text',
Doc View now creates a dedicated buffer to display it.  'C-c C-c' gets you
back to the real Doc View buffer if it still exists.

New commands to save and restore pages in buffer-local registers.
Doc View can store the current page to buffer-local registers with the new
command 'doc-view-page-to-register' (bound to 'm'), and later the stored
page can be restored with 'doc-view-jump-to-register' (bound to ''').

Doc View can generate imenu indices for DjVu and ODF documents.
When the 'djvused' program is available, Doc View can now generate an imenu
index for DjVu files from its outline.  Indices for Open Document Format
(ODF) files as used by OpenOffice and LibreOffice are generated using
the 'mutool' program after their initial conversion to PDF format.  The
name of the 'djvused' program can be customized by changing the user
option 'doc-view-djvused-program'.

Ispell

Emacs’s spell checker. I like M-x flyspell-mode (and M-x flyspell-prog-mode for programming that just does comments and strings) as they add squiggly lines to misspellings, and of course M-$ to spell check the word at point.

The default value of 'ispell-help-timeout' has changed.
The default value is now 30 seconds, as the old value was too short to
allow reading the help text.

Ispell can now save spelling corrections as abbrevs.
In the Ispell command loop, type 'C-u' immediately before selecting a
replacement to toggle whether that correction will be saved as a global
abbrev expansion for its misspelling.  The new user option
'ispell-save-corrections-as-abbrevs' determines whether abbrev saving
is enabled by default.

Oh that’s awesome. My article on Correcting Typos and Misspellings with Abbrev talks about how i turned Wikipedia’s list of common misspellings into abbrevs. I use it every day, without really knowing. It just… silently corrects typos.

Flyspell

As mentioned, this gives you squiggly underlines when you misspell something.

New user option 'flyspell-delay-use-timer'.
By default, Flyspell waits after so-called "delayed" commands by calling
'sit-for'.  If you customize this option to non-nil, Flyspell instead
sets up a timer to perform spell-checking after a short delay, which
allows idle timers and other code to run during this delay period.  We
plan to make this behavior the default in a future Emacs release, so we
invite Flyspell users to enable this new option and report any issues.

'turn-on-flyspell' and 'turn-off-flyspell' are obsolete.
To unconditionally enable 'flyspell-mode' from a hook, use this instead:

    (add-hook 'text-mode-hook #'flyspell-mode)

Tramp

Emacs’s system of communicating and interfacing with remote systems via Docker containers, Kubernetes, SSH, Android debug bridge and so many more. Truly one of the greatest features in Emacs.

Tramp signals 'remote-file-error' in case of connection problems.
This is a subcategory of 'file-error'.  Therefore, all checks for
'file-error' in 'condition-case', 'ignore-error', 'error-conditions' and
the like still work.

New command 'tramp-cleanup-bufferless-connections'.
Connection-related objects for which no associated buffers exist, except
for Tramp internal buffers, are flushed.  This is helpful to prune
connections after you close remote-file buffers without having to either
cherry-pick via 'tramp-cleanup-connection' or clear them all via
'tramp-cleanup-all-connections'.

External methods can now be used in multi-hop connections.
This is implemented for 'tramp-sh' methods, like "/scp:user@host|sudo::".

New command 'tramp-dired-find-file-with-sudo'.
This command, bound to '@' in Dired, visits the file or directory on the
recent Dired line with superuser, or root, permissions.

I already have a little helper command called sudo that does just this for files and dired buffers. Very welcome addition though. Remember this should work with multi-hops also.

'C-x x @' is now bound to 'tramp-revert-buffer-with-sudo'.
You can use 'C-u C-x x @' to select a Tramp method other than the
default, "sudo".

As above, this is genuinely great. I like that you can pick something other than sudo.

'tramp-file-name-with-method' can now be set as connection-local variable.

New optional connection methods "surs" and "sudors".
These connection methods are similar to "su" and "sudo", but they use
the modern 'su-rs' and 'sudo-rs' commands.

Connection method "kubernetes" now supports an optional namespace.
The host name for Kubernetes connections can be of kind
"[CONTAINER.]POD[%NAMESPACE]", in order to specify the namespace to be
used.  This overrides the setting in 'tramp-kubernetes-namespace', if
any.

Different proxies for the same destination host name can be specified.
A typical example are docker containers, which run on different hosts
under the same docker name.  When the user option
'tramp-show-ad-hoc-proxies' is non-nil, such ad-hoc multi-hop file names
can be used in parallel.  Example: on both remote hosts "host1" and
"host2" there is a docker container "name", respectively:

    /ssh:user1@host1|docker:name:
    /ssh:user2@host2|docker:name:

This feature is experimental.

Wonderful stuff. Tramps works with podman also so I expect it’ll work with those too.

Implementation of filesystem notifications for connection method "smb".

Remote process support has been rewritten for the "smb" connection method.
For more information, see "(tramp) Running remote processes on MS
Windows hosts" in the Tramp manual.

New functions to extend the set of operations with a remote implementation.
The new functions 'tramp-add-external-operation' and
'tramp-remove-external-operation' allow adding an implementation for
other operations than the defined set of magic file name operations.
This can be used by external ELPA packages for performance optimizations
in special cases.  For more information, see "(tramp) New operations" in
the Tramp manual.

New user option 'tramp-propagate-emacsclient-tramp'.
When this option is non-nil, Tramp propagates the environment variable
EMACSCLIENT_TRAMP with a proper value to remote processes.  This is
helpful if you want to start emacsclient on a remote host from a process
started inside Emacs.

Isearch and Replace

Isearch is Emacs’s interactive search bound to C-s. Replace is of course replacing text; Emacs has many of those too.

Typing 'd' during 'query-replace' shows the diff buffer with replacements.

Neat. Pair it with project-wide replacement like C-x p r to make sure you did not replace stuff you should not have.

Diff

.diff files, modes and related things. Emacs has a bunch of this stuff in various guises.

'diff-mode' now refrains from automatically refining big hunks.
What is big is defined by the new 'diff-refine-threshold' user option.

Refining a hunk shows a shadow cursor at the beginning/end of region.
By default, the shadow cursor looks like an empty rectangle the size of
a character cell.  It is displayed at the beginning or the end of the
refined region, to better show where the refined region starts or ends.
This can be controlled by the new user option
'smerge-refine-shadow-cursor', which also affects SMerge mode.

New command 'diff-kill-ring-save'.
This command copies to the 'kill-ring' a region of text modified
according to diffs in the current buffer, but without applying the diffs
to the original text.  If the selected range extends beyond a hunk, the
command attempts to look up and copy the text in between the hunks.

Ha that’s really cool. I like that I can now copy the patched diff hunk from a buffer. The challenge will be in remembering the command; this is not something I have to do frequently.

New command 'diff-revert-and-kill-hunk' bound to 'u' and 'C-c M-u'.
This command reverts the hunk at point (i.e., applies the reverse of the
hunk), and then removes the hunk from the diffs.
This is useful to undo or revert changes, committed and uncommitted, when
you are in buffers generated by 'C-x v =' and 'C-x v D'.
When the region is active, the command reverse-applies and kills hunks
that the region overlaps.

Oh yeah that’s awesome. I use Magit but I honestly prefer VC mode for in-buffer VC actions, so C-x v = and friends I use a lot.

'v' is now bound to 'vc-next-action' in read-only Diff mode buffers.

's' is now bound to 'diff-split-hunk' in read-only Diff mode buffers.

'diff-file-prev' and 'diff-hunk-prev' always move to start of header.
Previously, 'diff-file-prev' and 'diff-hunk-prev' would move when point
is after the corresponding file or hunk header, but not when inside it.
Now they will always move to the start of the current header.

New command 'diff-delete-other-hunks' bound to 'C-c RET n'.
This command deletes all hunks other than the current hunk.  It is
useful to prepare a "*vc-diff*" buffer for committing a single hunk.
When the region is active, it deletes all hunks that the region does not
overlap.

'vc-version-diff' and 'vc-root-version-diff' changed default for REV1.
They now suggest the previous revision as the default for REV1, not the
last one as before.  This makes them different from 'vc-diff' and
'vc-root-diff' when those are called without a prefix argument.

'diff-apply-hunk' now supports creating and deleting files.
'diff-apply-buffer' supports creating files but not deleting them, yet.

Diff mode's application and killing commands now consider the region.
If the region is active, 'diff-apply-hunk', 'diff-apply-buffer' and
'diff-hunk-kill' now apply or kill all hunks that the region overlaps.
Otherwise, they have their existing behavior.

'diff-apply-buffer' can reverse-apply.
With a prefix argument, it now reverse-applies hunks.
This matches the existing prefix argument to 'diff-apply-hunk'.

Ediff

Ediff is a 3-way interactive merge tool in Emacs. It’s excellent but it will take a little getting used to.

Ediff's copy commands now apply to all changes with 'C-u' prefix.
The Ediff copy commands, bound to 'a', 'b', 'ab', etc., now copy all
changes when supplied with a universal prefix argument via 'C-u':

- 'C-u a' copies all changes from buffer A to buffer B (in a 2-way diff)
  or to buffer C (in a 3-way diff or merge).
- 'C-u b' copies all changes from buffer B to buffer A (in a 2-way diff)
  or to buffer C (in a 3-way diff or merge).
- 'C-u a b' copies all changes from buffer A to buffer B.
- 'C-u b a' copies all changes from buffer B to buffer A.
- 'C-u a c' copies all changes from buffer A to buffer C.
- 'C-u b c' copies all changes from buffer B to buffer C.
- 'C-u c a' copies all changes from buffer C to buffer A.
- 'C-u c b' copies all changes from buffer C to buffer B.

Ediff now supports more flexible custom window layouts.
Custom implementations of 'ediff-window-setup-function' no longer need
to display all Ediff windows.  Any of the A, B, C, and control windows
can be left undisplayed and the corresponding variable set to nil.
This change enables custom layouts without a control panel window.

Dired

Dired is Emacs’s superlative directory editor and file browser. It has a wide range of advanced features. See Dired Shell Commands: The find & xargs replacement, WDired: Editable Dired Buffers and Working with multiple files in dired.

New user option 'dired-create-empty-file-in-current-directory'.
When non-nil, 'dired-create-empty-file' creates a new empty file and
adds an entry for it (or its topmost new parent directory if created)
under the current subdirectory in the Dired buffer by default
(otherwise, it adds the new file (and new subdirectories if provided) to
whichever directory the user enters at the prompt).  When nil,
'dired-create-empty-file' acts on the default directory by default.

Note that setting this user option to non-nil makes invoking
'dired-create-empty-file' outside of a Dired buffer signal an error
(like other Dired commands that always prompt with the current
subdirectory, such as 'dired-create-directory').

New user option 'dired-check-symlinks' allows disabling validity checks.
Dired uses 'file-truename' to check symbolic link validity when
fontifying them, which can be slow for remote directories.  Setting
'dired-check-symlinks' to nil disables these checks.  The new option
defaults to t and can be set as a connection-local variable.

New user option 'dired-hide-details-hide-absolute-location'.
When Dired's 'dired-hide-details-mode' is enabled, also hide the
'default-directory' absolute location, typically displayed as the first
line in a Dired buffer.

With 'dired-hide-details-hide-absolute-location':

    project: (100 GiB available)

Without 'dired-hide-details-hide-absolute-location':

    /absolute/path/to/my/important/project: (100 GiB available)

Clicking on the base name of a directory reverts the buffer.
When 'dired-make-directory-clickable' is non-nil, clicking on the base
name of the directory now reverts the Dired buffer.

'dired-copy-filename-as-kill' supports project-relative names.
With a prefix argument value of 1, this command now copies file names
relative to the root directory of the current project.

Lovely, but gated behind a prefix value of 1 makes it very utilitarian and hard to find without reading the docstring.

Warning when Dired displays a file name with a literal newline.
If Dired uses an 'ls' implementation that supports the '-b' switch, then
on visiting a directory that contains a file whose name has a newline,
and Dired displays that character as a literal newline, Emacs now
automatically pops up a buffer warning that such a display can be
problematic for Dired and showing a way to change the display to use the
unproblematic character '\n'.

Dired (except on Windows and other such platforms where it is emulated) uses the output of ls to furnish the dired buffer with its directory information. That is why stuff like my Dired Shell Commands: The find & xargs replacement that show you how to use find-name-dired and friends is so powerful. It’s just a buffer with text enriched with Emacs commands, font locking and such. Such a powerful concept

See Why Emacs has Buffers.

New user option 'dired-auto-toggle-b-switch'.
When this user option is non-nil and Dired uses an 'ls' implementation
that supports the '-b' switch and 'dired-listing-switches' does not
include the '-b' switch, then on visiting a directory containing a file
whose name has a newline, Emacs automatically adds the '-b' switch and
redisplays the directory in Dired to show '\n' in the file name instead
of a literal newline.  This prevents executing many Dired operations on
such a file from failing and signaling an error.  The default value of
this user option is nil.

New Dired handling of errors from 'ls'.
When invoking a Dired command causes 'ls' to emit an error message,
Emacs now displays the message in a popped up buffer instead of
outputting it in the Dired buffer and signalling an error.

Grep

Grep refers to Emacs’s wide range of grep wrapper commands. Note that you don’t have to use grep with them; you can of course change the tool to something else.

Grep results can be edited to reflect changes in the originating file.
Like Occur Edit mode, typing 'e' in the "*grep*" buffer will now make
the 'grep' results editable.  The edits will be reflected in buffers
visiting the originating files.  Typing 'C-c C-c' will leave the Grep
Edit mode.

Wonderful. Decades ago I wrote a little “extract” tool to do something similar as I often had to do precision edits across many files. This would’ve saved me a lot of time back in the day.

Occur edit mode is another feature most people sleep on. Do try out M-s o occur to match stuff, and then edit it with e. Occur works with multiple buffers but it does need a little encouragement.

Imenu

Imenu is Emacs’s generic selection interface for contextually interesting things in the current buffer: functions, classes, markdown headings, org mode headings, etc.

For decades it had no key binding. Now it’s bound to M-g i. I use M-i because that has a worthless default command.

New user option 'imenu-allow-duplicate-menu-items'.
This specifies whether Imenu can include duplicate menu items.
Duplicate items are now allowed by default (option value t), which
restores the behavior before Emacs 29.  Customize this to nil to get the
behavior of Emacs 29 and Emacs 30.

Time Stamp

You don’t see it as much any more, but back in the day people would commonly update files (Changelogs, source code files, etc.) with the timestamp of when the file was last changed. I’m not saying it’s not needed any more, but source control in many ways supplanted the need for it. But if you still want Emacs to find and update time stamps, you can with M-x time-stamp, though you’ll want a hook on before save to ensure changes are applied automatically.

'time-stamp' can up-case, capitalize and down-case date words.
This control can be useful in languages in which days of the week and/or
month names are capitalized only at the beginning of a sentence.  For
details, see the built-in documentation for user option 'time-stamp-format'.

Because this feature is new in Emacs 31.1, do not use it in the local
variables section of any file that might be edited by an older version
of Emacs.

Some historical 'time-stamp' conversions now warn.
'time-stamp-pattern' and 'time-stamp-format' had quietly accepted
several 'time-stamp' conversions (e.g., "%:y") that have been deprecated
since Emacs 27.1.  These now generate a warning with a suggested
migration.

Merely having '(add-hook 'before-save-hook #'time-stamp)'
in your Emacs init file does not expose you to this change.
However, if you set 'time-stamp-format' or 'time-stamp-pattern'
with a file-local variable, you may be asked to update the value.

TeX modes

TeX and friends. I recommend AUCTeX to anybody serious about writing LaTeX especially in Emacs.

New Xref backend for TeX modes.
The new backend ('tex-etags') is on by default, and improves the
functionality of the standard Xref commands in TeX buffers.  You can
restore the standard 'etags' backend with the 'xref-etags-mode' toggle.

Xref of course is Emacs’s generic cross-referencing feature that surfaces matches against search terms. Note again the “etags” here; back in the day, Emacs’s only real cross-referencing system was the wrapper around the external TAGS app. For compatibility with it, there are shims that try to serve both systems.

BibTeX mode

New user options facilitate customization of BibTeX and biblatex entries.
Entry definitions via the user options 'bibtex-BibTeX-aux-entry-alist',
'bibtex-biblatex-aux-entry-alist', 'bibtex-BibTeX-aux-opt-alist', and
'bibtex-biblatex-aux-opt-alist' take precedence over
'bibtex-BibTeX-entry-alist' and 'bibtex-biblatex-entry-alist'.
These user options now support the definition of aliases that inherit
the definition of another entry.

'bibtex-user-optional-fields' has been renamed to 'bibtex-aux-opt-alist'.
The old name is an obsolete alias.

'bibtex-include-OPTkey' is now obsolete and its default is nil.
Use 'bibtex-aux-opt-alist' instead.

New user option 'bibtex-entry-ask-for-key'.
When non-nil, 'bibtex-entry' asks for a key.

'bibtex-string-file-path' and 'bibtex-file-path' are lists of directories.
For backward compatibility, considered obsolete, these user options
may still be strings of colon-separated lists of directories.

Midnight mode

Midnight mode is a garbage collector for buffers that runs, well, around midnight, or at a time of your choosing. It is well worth using, in my opinion, but watch your six: you want it to delete trash buffers and never anything important. It comes with a quite conservative (and to me mostly useless) set of defaults

My setting looks like this:

(use-package midnight
  :custom ((midnight-mode 1)
           (clean-buffer-list-delay-general 5)
           (clean-buffer-list-kill-buffer-names
            '("*Buffer List*" "*Compile-Log*" "*vc*" "*vc-diff*" "*diff*" "*gnus work*" "*Backtrace*"))
           (clean-buffer-list-kill-regexps (list (rx bos (? " ") (| "*magit" "magit-" "*Customize" "*mm*-")))))
  :config
  (midnight-delay-set 'midnight-delay 6400))

Change for activating the mode.
Putting '(require 'midnight)' in your init file no longer activates the
mode.  Now, one needs to customize 'midnight-mode' to non-nil or say
'(midnight-mode 1)', instead.

Python mode

Python, but note not the TS mode. If you’re a Python hacker try my Combobulate package.

New 'repeat-map' for Python indentation commands.
The commands 'python-indent-shift-left' and 'python-indent-shift-right'
can now be repeated using 'repeat-mode'.  With 'repeat-mode' enabled,
after invoking one of these commands via 'C-c <' or 'C-c >', you can
type '<' or '>' to repeat the command.

Prefer "python" for 'python-interpreter' and 'python-shell-interpreter'.
On recent versions of mainstream GNU/Linux distributions, "python"
either does not exist or it points to Python 3.  These user options now
default to using "python", falling back to "python3" if it does not
exist.  If "python" points to Python 2 on your system, you now need to
customize these variables to "python3" if you want to use Python 3
instead.

Python 2 support is now optional and disabled by default.
Since Python 2 EOL was over 5 years ago, this release removes Python
2-only builtins such as "file" from the default highlighting in
'python-mode' and 'python-ts-mode'.  If you would like them highlighted,
customize the new user option 'python-2-support' to a non-nil value and
restart Emacs.

New Python support for 'electric-layout-mode'.

'DEL' can delete text in the active region.
When point is between indentation, the command
'python-indent-dedent-line-backspace' (by default bound to 'DEL') now
deletes the text in the region and deactivates the mark if Transient
Mark mode is enabled, the mark is active, and the value of the prefix
argument is 1.

Mmm, no, thank you. Python is a twitchy whitespace language. And heuristic whitespace deletion across multiple lines possible? Nah.

'python-eldoc-function-timeout' now accepts floating-point numbers.
To allow for finer-grained adjustment of timeout for
'python-eldoc-function', 'python-eldoc-function-timeout' now accepts
floating-point numbers as well as integers.

But why is that a python-only construct?

The default value of 'python-shell-completion-setup-code' is changed.
A new function is added to the setup code.  Users who modify this option
may need to update the value for the Python shell completion to work.

Tmm Menubar

This is an in-buffer emulation of Emacs’s menu-bar-mode using a modal-like system that is reminiscent of what Magit would eventually end up looking like, sort of. It’s one of several ways of opening the menu bar (M-x menu-bar-open being another)

New shortcut '^' to navigate to the previous menu.

New user option 'tmm-shortcut-inside-entry'.
When non-nil, highlight the character shortcut in the menu entry's
string instead of prepending it and 'tmm-mid-prompt' to said entry.

Foldout

Outline-mode, which is what Org (was? is?) based off of back in the day as an outliner, has a number of extensions. foldout is one of them; it is not autoloaded by default.

Improved behavior of 'foldout-exit-fold' with a negative prefix argument.
When 'foldout-exit-fold' is called with a negative argument (so that the
exited fold remains visible), the position of point and window view are
preserved.

New command 'foldout-widen-to-current-fold'.
This command widens the view to the current fold level when in a fold,
or behaves like 'widen' if not in a fold.

MPC

MPC is a thin wrapper around the MPC daemon, a music player. I have never used it. I recommend EMMS if you want something with a wider reach: there are spotify plugins and all sorts for it.

New user option 'mpc-notifications'.
When non-nil, MPC (the Emacs front-end to Music Player Daemon) displays
a desktop notification when the song changes, using
'notifications-notify'.  The notification's title and body can be
customized using the new user options 'mpc-notifications-title' and
'mpc-notifications-body'.

New user option 'mpc-crossfade-time'.
When non-nil, MPC will crossfade between songs for the specified number
of seconds.  Crossfading can be toggled using the command
'mpc-toggle-crossfade' or from the MPC menu.

New command 'mpc-describe-song'.
This command displays information about the currently playing song or
song at point in the "*MPC-Songs*" buffer.  The list of tags to display
can be customized using the new user option 'mpc-song-viewer-tags' and
the appearance of the list with the new faces 'mpc-table-key',
'mpc-table-value', and 'mpc-table-empty'.

New command 'mpc-server-stats'.
This command displays information about the connected MPD server.  The
appearance of the list can be customized with the new faces
'mpc-table-key' and 'mpc-table-value'.

VC

VC is Version Control, a wrapper around a slew of version control systems, including git, subversion, hg and many more. I really rate it. Before Magit/git became a thing, it was a life saver, abstracting away the tedium of each VCS into a set of common key bindings.

Honestly, between me you and the lamp post, as VC gains more and more functionality, I find I reach for Magit less and less. I always preferred the way VC works.

Printing root branch logs has moved to 'C-x v b L'.
Previously, the command to print the root log for a branch was bound to
'C-x v b l'.  It has now been renamed from 'vc-print-branch-log' to
'vc-print-root-branch-log', and bound to 'C-x v b L'.  This is more
consistent with the rest of the 'C-x v' keymap, and makes room for a new
fileset-specific branch log command.

To undo this change you can use

    (keymap-global-set "C-x v b l" #'vc-print-root-branch-log)
    (with-eval-after-load 'vc-dir
      (keymap-set vc-dir-mode-map "b l" #'vc-print-root-branch-log))

New command 'C-x v b l' ('vc-print-fileset-branch-log').
This command prints the log of VC changes to the current fileset on
another branch.

VC Annotate for Mercurial repositories shows changeset hashes.
To restore showing revision numbers instead of changeset hashes,
customize the new user option 'vc-hg-annotate-show-revision-numbers' to
non-nil.

'vc-hg-working-revision' now returns changeset hashes.
Previously, it returned local revision numbers, but hashes are more
robust for how this function is typically used.

New commands to handle repositories with multiple working trees.
Some VCS support more than one working tree with the same backing
revisions store, such as with Git's 'worktree' subcommand and
Mercurial's 'share' extension.  Emacs now has some commands to manage
other working trees:

- 'C-x v w c': Add a new working tree.
- 'C-x v w w': Visit this file in another working tree.
- 'C-x v w k': Kill buffers visiting this file in other working trees.
- 'C-x v w s': Like 'C-x p p' but limited to other working trees.
- 'C-x v w a': Copy or move fileset changes to another working tree.
- 'C-x v w A': Copy or move all changes to another working tree.
- 'C-x v w x': Delete a working tree you no longer need.
- 'C-x v w R': Relocate a working tree to another file name.

The new user option 'vc-no-confirm-moving-changes' controls whether
'C-x v w a' and 'C-x v w A' ask for confirmation when moving changes
between working trees.  The default is to ask for confirmation.

In addition, Lisp programs that extend VC can invoke the new backend
functions to obtain a list of other working trees, and to add, remove
and relocate them.

Worktrees are becoming a lot more popular because of AI development in particular. I won’t lie: git’s worktrees suck, but at least it has some level of support for shallow copying a repository. I’m glad VC has added a generic wrapper system on top of it. I will have to experiment with it.

Using 'e' from Log View mode to modify change comments now works for Git.

New user option 'vc-allow-rewriting-published-history'.
Some VCS commands can change your copy of published change history
without warning.  In VC we try to detect before that happens, and stop.
You can customize this option to permit rewriting history even though
Emacs thinks it is dangerous.

'vc-clone' is now an interactive command.
When called interactively, 'vc-clone' now prompts for the remote
repository address, and the directory into which to clone the
repository.  It tries to automatically determine the VC backend for
cloning, or prompts for that, too.

Useful. VC is weird like that; it’s surprisingly feature rich, and yet it is often missing little convenience features like this.

'vc-clone' now accepts an optional argument OPEN-DIR.
When the argument is non-nil, the function switches to a buffer visiting
the directory into which the repository was cloned.

'vc-revert' is now bound to '@' in VC Directory.

C-x v d asks your VCS to show a directory overview. It’s the focal point of Emacs’s VC in many ways.

'vc-revert' is now additionally bound to 'C-x v @'.
This is in addition to 'C-x v u'.

'vc-rename-file' is now bound to 'C-x v R'.

'vc-revert' now works on directories listed in VC Directory.
Reverting a directory means reverting changes to all files inside it.

New global minor mode 'vc-auto-revert-mode'.
This is like 'global-auto-revert-mode' but limited to VCS-tracked files.
As compared with VC's existing, default support for reverting files
after VCS operations, the new mode is a more reliable way to ensure that
Emacs reverts buffers visiting tracked files when VCS operations change
the contents of those files.

New commands to cherry-pick and revert revisions.
The commands 'vc-cherry-pick', 'vc-revert-or-delete-revision',
'vc-revert-revision' and 'vc-delete-revision' let you copy revisions
between branches, revert and delete revisions.
From Log View buffers, you can use 'C' to cherry-pick the revision at
point or all marked revisions, and 'R' to undo the revision at point or
all marked revisions.

New commands to rewind branches.
In Log View mode, 'x' deletes revisions newer than the revision at point
from the history of the current branch, though without undoing the
changes made by those revisions to the working tree.  'X' is similar
except that it does remove the changes from the working tree.

New command 'log-edit-done-strip-cvs-lines'.
This command strips all lines beginning with "CVS:" from the buffer.
It is intended to be added to the 'log-edit-done-hook' so that
'vc-cvs-checkin' behaves like invoking 'cvs commit [files...]' from the
command line.

New user options 'vc-resolve-conflicts' and 'vc-*-resolve-conflicts'.
They control whether to mark a conflicted file as resolved when saving.
You can now control it globally, with 'vc-resolve-conflicts', or for
specific backends with 'vc-bzr-resolve-conflicts',
'vc-hg-resolve-conflicts', and 'vc-svn-resolve-conflicts'.

New value for 'vc-git-resolve-conflicts'.
The option now accepts the symbol 'default' as a value, which is
its default value.  Effectively, the default value hasn't changed,
since 'vc-resolve-conflicts' defaults to t, the previous default value
for 'vc-git-resolve-conflicts'.

VC Directory can now automatically add and remove marks on other lines.
When you try to use a mark or unmark command where doing so would
be permitted only if other lines were marked or unmarked first, Emacs
will now ask you if you'd like to change the marks on those other lines.
For example, if you try to mark a file contained within a directory that
is already marked, Emacs will offer to unmark the directory, first.
Previously, Emacs would simply refuse to make any changes.
You can customize 'vc-dir-allow-mass-mark-changes' to restore the old
behavior or dispense with the prompting.

'C-x v x' and VC Directory's 'd' command can now delete unregistered files.
Previously, these commands could only delete registered files.
To restore the old, more limited behavior for VC Directory, you can do

    (keymap-set vc-dir-mode-map "d" #'vc-dir-clean-files)

New VC Directory bindings 'z d' and 'D' to delete Git stashes.
These correspond to the existing 'z p' to pop a stash and 'P' to pop the
stash at point (deleting the stash at point is also bound to 'C-k').

New VC Directory command 'V' ('vc-dir-root-next-action').
This is like 'v' ('vc-next-action') but applies to the whole VC Directory
buffer, ignoring the position of point and any marks.  This is useful to
check in all local changes at once.

VC Directory can now register files when checking in mixed filesets.
Previously, if some files to be checked in were unregistered but others
were added, removed or edited, Emacs would refuse to proceed.
Now Emacs prompts to register the unregistered files, so that all
files in the fileset are in a compatible state for a checkin.

'C-x v v' handles missing and removed files more consistently.
Missing files are those which have been removed from the filesystem but
which are still tracked by version control.  Removed files are those
scheduled to be removed from version control in the next commit.
Previously, different backends were inconsistent about applying these
statuses to files, and 'C-x v v' behaved subtly differently for the two
statuses.  The combination of these differences between backends and in
'C-x v v' behavior was confusing.  Now,

- in VC Directory, you can use 'C-x v v' on missing files to mark them as
  removed
- when committing, you can include missing files in a set of files with
  different statuses, just like you've always been able to include
  removed files.

In addition, the Git backend has been fixed to display missing files as
'missing' instead of incorrectly subsuming them to the 'removed' status.

There is still some further work to do to rationalize VC's handling of
file removal.

C-x v v is the workhorse command. It does the next logical action: add a file; commit changes; etc.

New user option 'vc-dir-auto-hide-up-to-date'.
If you customize this option to 'revert', the 'g' command to refresh
the VC Directory buffer also has the effect of the 'x' command.
That is, typing 'g' refreshes the buffer and also hides items in the
'up-to-date' and 'ignored' states.
If you customize this option to any other non-nil value, then in
addition, hide items whenever their state would change to 'up-to-date'
or 'ignored'.

New user option 'vc-dir-save-some-buffers-on-revert'.
If you customize this option to non-nil, Emacs will offer to save
relevant buffers before generating the contents of a VC Directory buffer
(like the third-party package Magit does with its status buffer).

New commands to report incoming and outgoing diffs.
'vc-root-diff-incoming' and 'vc-root-diff-outgoing' report diffs of all
the changes that would be pulled and would be pushed, respectively.
They are the diff analogues of the existing commands
'vc-root-log-incoming' and 'vc-root-log-outgoing'.

In particular, 'vc-root-diff-outgoing' is useful as a way to preview
your push and ensure that all and only the changes you intended to
include were committed and will be pushed.

'vc-diff-incoming' and 'vc-diff-outgoing' are similar but limited to the
current VC fileset.

New commands to report information about unintegrated changes.
'C-x v T =' ('vc-diff-unintegrated') and 'C-x v T D'
('vc-root-diff-unintegrated') report diffs of changes since the merge
base with the remote branch, including uncommitted changes.
'C-x v T l' ('vc-log-unintegrated') and 'C-x v T L'
('vc-root-log-unintegrated') show the corresponding revision logs.
These are useful to view all outstanding (unmerged, unpushed) changes on
the current branch.  They are also available as 'T =', 'T D', 'T l' and
'T L' in VC Directory buffers.

'C-x v T R =' ('vc-diff-remote-unintegrated'), 'C-x v T R D'
('vc-root-diff-remote-unintegrated'), 'C-x v T R l'
('vc-log-remote-unintegrated') and 'C-x v T R L'
('vc-root-log-remote-unintegrated') are corresponding commands which
report information about the remote versions of a topic branch.

Ah this is really useful. I’ll have to experiment with them and see if they present things in a more useful way than Magits’. One common problem I often have with work is that I do a lot of work in worktrees nowadays. I’ve built out some shell scripts to see how far ahead/behind they are, and whether they cleanly merge. So it’d be nice if I can re-use some of the code here maybe to do that.

New commands to report combined diffs of all local changes.
'C-x v E =' ('vc-diff-outgoing-and-edited') and 'C-x v E D'
('vc-root-diff-outgoing-and-edited') report combined diffs of all
outgoing changes plus any uncommitted changes.  They are useful to show
all work that's present only locally.

New user option 'vc-use-incoming-outgoing-prefixes'.
If this is customized to non-nil, 'C-x v I' and 'C-x v O' become prefix
commands, such that the new incoming and outgoing commands have global
bindings:

- 'C-x v I L' is bound to 'vc-root-log-incoming'
- 'C-x v I =' is bound to 'vc-diff-incoming'
- 'C-x v I D' is bound to 'vc-root-diff-incoming'
- 'C-x v O L' is bound to 'vc-root-log-outgoing'
- 'C-x v O =' is bound to 'vc-diff-outgoing'.
- 'C-x v O D' is bound to 'vc-root-diff-outgoing'.

New display of outgoing revisions count in VC Directory.
If there are outgoing revisions, VC Directory now includes a count of
how many in its headers, to remind you to push them.  If this is slow,
you can disable it by customizing 'vc-dir-show-outgoing-count' to nil.
(In Emacs 32 it will be populated asynchronously.)

New user option 'vc-async-checkin' to enable async checkin operations.
Currently only supported by the Git and Mercurial backends.

New user option 'vc-display-failed-async-commands'.
If non-nil, displays the buffer with the output of the failed command
when an asynchronous VC command (e.g., pulls and pushes) fails.

New 'log-edit-hook' option to display diff of changes to commit.
You can customize 'log-edit-hook' to include its new
'log-edit-maybe-show-diff' option to enable displaying a diff of the
changes to be committed in a window.  This is like the 'C-c C-d' command
in Log Edit mode buffers, except that it does not select the "*vc-diff*"
buffer's window, and so works well when added to 'log-edit-hook'.

'vc-annotate' now abbreviates the Git revision in more cases.
In Emacs 30, 'vc-annotate' gained the ability to abbreviate the Git
revision in the buffer name.  Now, it also abbreviates the Git revision
when visiting other revisions, such as with
'vc-annotate-revision-previous-to-line'.

New buffer-local variable 'vc-buffer-overriding-fileset'.
Primarily intended for buffers not visiting files, this specifies the
VC backend and VCS-managed file name or file names to which the buffer's
contents corresponds.  It overrides the behavior of 'vc-deduce-fileset'.
This replaces and generalizes the old 'vc-annotate-parent-file'.

New buffer-local variable 'vc-buffer-revision'.
This specifies the revision to which the buffer's contents corresponds.
This replaces and generalizes the old 'vc-annotate-parent-rev'.

The 'log-incoming' and 'log-outgoing' functions are deprecated.
Backend authors should implement the 'incoming-revision' and 'mergebase'
backend functions instead.  These are jointly sufficient to support the
'C-x v I' and 'C-x v O' commands.

Marking revisions in Log View now works more like other modes.
Previously, 'm' toggled whether the current revision was marked, and
didn't advance point.  Now 'm' only adds marks, 'u' removes marks, and
both advance point, like how marking works in Dired and VC Directory.
You can get back the old behavior with something like this:

    (with-eval-after-load 'log-view
      (keymap-set log-view-mode-map "m" #'log-view-toggle-mark-entry))

In addition, a new command 'U' removes all marks.

New commands 'M-RET', 'M-p' and 'M-n' in Log View mode.
'M-RET' expands the current entry, if relevant, and displays its diff in
another window.  'M-p' and 'M-n' move to the previous and next entries,
respectively, expand them if relevant, and display their diffs.

You can use these three commands together to more easily view all the
log entries and diffs of a series of revisions: use 'M-RET' on the first
revision, then either 'M-n' or 'M-p' repeatedly to view the others.

Log view (C-x v l) is a feature (along with C-x v = for a diff of changes in the current buffer) that I use the most. They work anywhere and give me immediate insight into changes in a file.

New command 'w' in Log View mode.
The new command 'log-view-copy-revision-as-kill', bound to 'w' in Log
View mode, copies to the kill ring the ID of the revision at point in
the log entry.  If there are marked revisions, it copies the IDs of
those, instead.

New commands 'vc-print-change-log' and 'vc-print-root-change-log'.
These are just like 'vc-print-log' and 'vc-print-root-log' except that
they have a different prefix argument that some users may prefer.
With a prefix argument, these commands prompt for a branch, tag or other
reference to a revision to log, and a maximum number of revisions to
print.  If you find this prefix argument more useful, or more mnemonic,
than the prefix arguments that 'vc-print-log' and 'vc-print-root-log'
already have, consider replacing the default global bindings, like this:

    (keymap-global-set "C-x v l" #'vc-print-change-log)
    (keymap-global-set "C-x v L" #'vc-print-root-change-log)

New command alias 'vc-restore' for 'vc-revert'.

The 'diff-restrict-view' command is disabled by default.
This command is Diff mode's specialized 'narrow-to-region'.
'narrow-to-region' has long been disabled by default, so for
consistency, 'diff-restrict-view' is now too.
To enable it again, use 'enable-command'.

'C-x v !' now has its own input history.

'C-x v +' for Git pulls from a configured push remote.
If the current branch has a configured push remote, the default
arguments to 'git pull' will cause a pull from the push remote.
You can use 'C-u C-x v +' to preview or change the arguments.

'C-u C-x v +' and 'C-u C-x v P' for Git have an input history.
This was already in place for Mercurial.

vc-dav.el is now obsolete.

Package

Emacs’s package manager.

No longer warn if a package has no footer line.
package.el no longer warns for packages without a "footer line", which
is the line that usually appears at the very end of an Emacs Lisp file:

    ;;; FILENAME ends here

New optional argument to 'package-autoremove'.
An optional argument NOCONFIRM has been added to 'package-autoremove'.
If it is non-nil (interactively, with a prefix argument),
'package-autoremove' will not prompt the user for confirmation before
removing packages.

New prefix argument for 'package-install-selected-packages'.
When invoked with a prefix argument, 'package-install-selected-packages'
will not prompt the user for confirmation before installing packages.

'package-refresh-contents' runs asynchronously.
Refreshing the package index will no longer block when invoked
interactively.

'package-upgrade' no longer accepts a string argument.
When called from Lisp, it now only accepts a symbol.

'package-install-from-buffer' respects files marked by Dired.
When invoking the command in a Dired buffer with marked files,
the command will copy only those files.

'package-isolate' can now also install packages.
If a package is missing, 'package-isolate' will fetch the missing
tarballs and prepare them to be activated in the sub-process.

package-x.el is now obsolete.

The command 'package-vc-install-from-checkout' is now obsolete.
Use the User Lisp directory instead: see Info node "(emacs) User Lisp
Directory".  This also means that combining the 'use-package' keywords
':vc' and ':load-path' is obsolete.

Er… what. So the idea is that you put files in 31’s new user lisp directory, which is the feature I talked about earlier that finds and installs autoload cookies; byte compiles; etc.

And the idea here is that you just git clone or whatever in this directory instead of using the just recently added(!!) :vc feature in use-package.

But now that disconnects people who prefer colocating all their changes in use-package definitions. They now need the new user directory; a method of installing/cloning their packages into that directory; and at no point does that tie back to a use-package definition.

Bizarre change. Really bizarre.

Package menu now highlights packages marked for installation or deletion.

Package menu now displays the total number of the package type.
The package menu now displays in the mode line the total number of
packages installed, the total number of packages from all the package
archives, the total number of packages to upgrade and the total number
of new packages available.

New functions to query builtin package information.
'package-versioned-builtin-packages' returns a list of symbols of
built-in packages; 'package-builtin-package-version' returns the
version-list of a given package symbol.  These functions provide public
interfaces for external tools to query information about built-in
packages.

Uninstalling a package now removes its directory from 'load-path'.

Packages can be reviewed before installation or upgrade.
The user option 'package-review-policy' can configure which packages
the user should be allowed to review before any processing takes place.
The package review can include reading the downloaded source code,
presenting a diff between the downloaded code and a previous
installation or displaying a ChangeLog.

New command 'package-autosuggest'.
Using a built-in database of ELPA package suggestions, this command will
install viable packages if no specific major mode is available for the
contents of the current buffer.

That feels useful to people. Teach them about other useful packages…

New minor mode 'package-autosuggest-mode'.
When enabled, this displays indications about the availability of add-on
ELPA packages for the current buffer and suggestions for installing
those packages.  The default is to show a button on the mode line that
can be used to install such packages, but you can customize the
presentation style of these suggestions using
'package-autosuggest-style'.

Buuut of course it is not enabled by default.

New user option 'package-retention-policy'.
This user option controls what previous packages versions to keep on
upgrade.  By default, this is set to nil, to keep the previous behavior.

Packages are now checked for recursive dependencies before installing.
If a package has dependencies not available on any of the archives in
'package-archives', it will appear as unavailable, with the reasons
stated in its description.

Rcirc

One of two IRC clients in Emacs.

Authentication via NickServ can access auth source passwords.
For details, consult 'rcirc-authinfo'.

Xref

As I mentioned before, xref is Emacs’s cross-referencing implementation, and a replacement for the old TAGS finder system.

Xref commands that jump to some location use 'display-buffer'.
The commands that jump to some location use 'display-buffer' and specify
the category 'xref-jump'.  As a result, you can customize how the
destination window is chosen using 'display-buffer-alist'.  Example:

    (setq display-buffer-alist '(((category . xref-jump)
                                  (display-buffer-reuse-window
                                   display-buffer-use-some-window)
                                  (some-window . mru))))

Neat change. But of course it’s yet more complexity front-loaded into display-buffer-alist, probably the most complex variable in Emacs today. Basically when Emacs has to pick where a buffer goes, it goes through a cascading list of user-customized and predefined options with safe fallbacks. But display-buffer-alist (and therefore Emacs) has to be taught to show buffers in just the right way, or your customizations won’t apply.

But how can display-buffer-alist (or you, the customizer) know that a buffer that is about to appear came from xref? Well, you can’t… so there is a new (category N) selector that effectively says “if you come from an xref-jump, reuse a an existing window that displays this buffer; otherwise pick a window, but make sure that you pick the most-recently-used.”

Confused? See Demystifying Emacs’s Window Manager.

New minor mode 'xref-mouse-mode'.
This minor mode binds 'xref-find-definitions-at-mouse' to
'C-<down-mouse-1>', allowing you to control-click to jump to a
definition, following the convention from other editors.  The global
minor mode 'global-xref-mouse-mode' enables this in all buffers.

New command 'xref-change-to-xref-edit-mode'.
It is bound to 'e' and it switches an Xref buffer into an "editable"
mode, like similar features in Occur and Grep buffers.

Wonderful news. Editable buffers is such an Emacs-shaped feature to have, I was quite surprised when Xref first came out that it did not do this at all.

Revert

Variable 'revert-buffer-in-progress' has been renamed.
The old name, 'revert-buffer-in-progress-p', is kept as an obsolete
variable alias.  (Symbol names with a trailing '-p' are conventionally
reserved for predicates.)

Autorevert

The auto-revert-mode minor mode reverts a buffer when certain conditions are met: VC changes, file changed on the file system, and so on.

New variable 'inhibit-auto-revert-buffers'.
While a buffer is member of this variable, a list of buffers,
auto-reverting of that buffer is suppressed.

I actually thought Emacs already had this feature. So I am a little surprised that it only just made an appearance in Emacs 31.

I suspect most people won’t have an immediate use for this, as auto-revert is rather conservative about reversions.

New macro 'inhibit-auto-revert'.
This macro adds the current buffer to 'inhibit-auto-revert-buffers',
runs its body, and removes the current buffer from
'inhibit-auto-revert-buffers' afterwards.

New variable 'auto-revert-buffer-in-progress'.
'auto-revert-buffer' binds this variable to a non-nil value while it is
working.  This can be used by major mode 'revert-buffer-function'
implementations to suppress messages in Auto Revert modes, for example.

Strokes

Strokes is a mouse gesture recognition mode. Draw shapes with your mouse and you can trigger a range of actions. See M-x strokes-help.

'strokes-mode' no longer demands the presence of a mouse.
'strokes-mode' now permits itself to be enabled if no mouse is
connected, to facilitate enabling 'strokes-mode' in sessions where the
availability of a mouse device varies during execution (as is frequently
observed on Android).

Okay so the mouse thing no longer needs a mouse, but I can’t intuit if that means touch gestures now trigger it on android? Because that… seems like a natural fit for strokes-mode?

Yank Media

'yank-media' now auto-selects the most preferred MIME type.
Major-mode authors can customize the variables
'yank-media-autoselect-function' and/or 'yank-media-preferred-types' to
change the selection rules.

Most people know you can yank text with C-y; few know you can yank media (images in clipboard) with M-x yank-media. I use it with mu4e, the Emacs email client. In typical Emacs fashion, the yank-media command asks me a lot of useless information like whether I want to use mime type ppm or equally antique stuff when what I really want is just… you know, to insert an image? So this is a welcome change.

Remember

Remember is a bit like org-capture, but predates it. Pretty sure org mode can capture remember snippets for you also.

Remember mode is now a minor mode.
The 'remember' command enables the major mode set in
'remember-initial-major-mode' and then the 'remember-mode' minor mode in
the 'remember-buffer'.  This allows users to customize the major mode
used to write notes.

New handler that appends remember data in directory.
The 'remember-append-in-data-directory' handler appends remember data in
a file, that file being chosen by the user through the minibuffer.

New prefix map for remember commands.
Meant to be given a global binding convenient to the user.  Example:

    (keymap-global-set "C-c r" 'remember-prefix-map)

Speedbar

Speedbar is a file browser that pops up a frame. I never liked it: looks awful, opens a frame, hoards space, and tells me mostly-useless information: what is going on in a directory. I prefer dired for when I want to know what’s up in a directory, but I appreciate that many people do not agree with me here.

New commands for Speedbar.

- 'speedbar-window-mode' opens Speedbar in a window instead of a frame.
- 'speedbar-window' is an alias for 'speedbar-window-mode'.

About time. Speedbar got merged in as part of the CEDET large hadron collider event some 15 years ago and it’s sat there untouched ever since.

New user options for Speedbar.

- 'speedbar-prefer-window' tells 'speedbar' to open a side window
  instead of a frame.
- 'speedbar-window-dedicated-window' defines whether 'speedbar' is
  displayed in a dedicated window.
- 'speedbar-window-default-width' defines the initial width of the
  'speedbar-window'.
- 'speedbar-window-max-width' defines the maximum width of the
  'speedbar-window' when it is closed and then restored.

Ugh. I mean look I get that if you’re going to cram speedbar into a window, you probably want it flush in a sidebar (meaning it always appears in one of four edges of your frame) and that it should never share its window with another buffer (hence marking it dedicated.)

But Emacs already has a display buffer system for this; by adding weird variables (even if they edge-trigger and set a display-buffer-alist rule) you’re effectively creating the same two-tier system Emacs has spent 10 years trying to undo.

'speedbar-easymenu-definition-trailer' is now a function.

Icomplete

Icomplete is a fast completion system going back to the 90s. It saw a lot of updates as Emacs modernized its Minibuffer Completion system. Ido Mode is loosely inspired by/has borrowed code from icomplete.

Change in meaning of 'icomplete-show-matches-on-no-input' (again).
For Emacs 28 to Emacs 30, when 'icomplete-show-matches-on-no-input' was
non-nil, 'RET' had special behavior when the minibuffer's contents was
equal to the initial input it had right after minibuffer activation.
In that case, 'RET' would choose the first completion candidate, if
there was one, instead of the minibuffer's default value.
'RET' has now returned to selecting the default value in this case; you
can use 'C-j' to choose the completion under point instead.
You can opt back in to the special behavior of 'RET' like this:

    (keymap-set
      icomplete-minibuffer-map "<remap> <minibuffer-complete-and-exit>"
      #'icomplete-ret)

New user options for 'icomplete-vertical-mode'.
New user options have been added to enhance 'icomplete-vertical-mode':

- 'icomplete-vertical-in-buffer-adjust-list' aligns in-buffer
  completion to the original cursor column.
- 'icomplete-vertical-render-prefix-indicator' adds a prefix indicator
  to completion candidates.
- 'icomplete-vertical-selected-prefix-indicator' specifies the prefix
  string for the selected candidate.
- 'icomplete-vertical-unselected-prefix-indicator' specifies the prefix
  string for non-selected candidates.

New faces for 'icomplete-vertical-mode'.
New faces have been added to 'icomplete-vertical-mode':

- 'icomplete-vertical-selected-prefix-indicator-face' controls the
  appearance of the selected candidate prefix.
- 'icomplete-vertical-unselected-prefix-indicator-face' controls the
  appearance of unselected candidate prefixes.

Custom

Custom is Emacs’s customize interface and internal subsystems.

New function 'custom-initialize-after-file-load'.
Useful to delay initialization to the end of the file, so it can use
functions defined later than the variable, as is common for minor modes.
'define-globalized-minor-mode' now automatically uses it if the
':init-value' is non-nil.

Probably a sensible thing to enable if you’re a heavy Customize user.

New major mode 'Custom-dirlocals-mode'.
This is intended for customizing directory-local variables in the
current directory's ".dir-locals.el" file.

New binding 'C-c C-k' for 'Custom-reset-standard'.

New command 'C-c TAB' ('Custom-goto-first-choice').
When first opening the customization interface for a user option, you
can use this command as a shortcut to jump to the first actionable
button or field (for instance an on/off button for boolean options, or a
text field for other values).

':set' functions should accept an optional argument BUFFER-LOCAL.
This is the third argument, in addition to SYMBOL and VALUE.  If that
argument's value is 'buffer-local', the ':set' function should use
'set-local' to set the value of its SYMBOL argument locally in the
current buffer.  This is used by 'setopt-local', which will signal an
error if this optional argument is not supported by the ':set' function.

The 'defcustom' ':local' keyword can now be 'permanent-only'.
This means that the variable's 'permanent-local' property is set to t,
without marking it as automatically buffer-local.

Pulse

Another CEDET feature that landed in Emacs some 15 years ago. This one pulses stuff in the ui. Quite handy if a bit distracting, and now used in a wide range of things.

New user option 'pulse-face-duration'.
This option controls the flash duration for 'flash-face-bell-function'
and 'flash-echo-area-bell-function'.

New function 'pulse-faces'.
This function pulses a specified list of faces.  The pulse duration is
determined by the new user option 'pulse-face-duration'.

Edebug

Emacs’s Emacs Lisp debugger, written in (of course) Emacs Lisp. Not to be confused with the classic debug elisp debugger, of course.

New command 'edebug-bounce-to-previous-value' (bound to 'P').
This command temporarily displays the outside current buffer with the
outside point corresponding to the previous value, where the previous
value is what Edebug has evaluated before its last stop point or what
the user has evaluated in the context outside of Edebug.

This replaces the binding of command 'edebug-view-outside' to 'P', which
is still available on 'v'.

Flymake

Flymake is Emacs’s “on-the-fly” syntax/error/lint checker that highlights info, warnings and errors in the buffer.

Enhanced 'flymake-show-diagnostics-at-end-of-line'.
The new value for this user option 'fancy' attempts to lay out
diagnostics below the affected line, using unicode graphics to point to
the diagnostic locus.

Flymake is really a two-tier system. There’s the high-level overview: squiggly underlines, backgrounded text, etc. that tells you there is a reported issue. The second tier is the detail tier that tells you exactly what happens. You can opt for a popup buffer and/or eldoc integration.

Now there is a third. You can now tell Emacs to insert diagnostic messages flush in the buffer at the end of the line where the change occurred, like other IDEs.

I’m sure a lot of people will find it very useful, but it is not for me. Emacs’s overlay system is nice and all, but flickering text and stuff disappearin and reappearing as the flymake mode reruns will surely drive a lot of people crazy.

Enhanced 'flymake-show-buffer-diagnostics'.
The command 'flymake-show-buffer-diagnostics' is now capable of
highlighting a nearby diagnostic in the resulting listing.
Additionally, it is bound to mouse clicks on fringe and margin
indicators, operating on the diagnostics of the corresponding line.
You can bind it yourself in other situations too, such as in the
diagnostic overlay map.

More powerful 'flymake-make-diagnostic' API.
Flymake backends can now specify origin and code attributes, allowing
Flymake and other extensions to segregate diagnostics based on this
extended information.

New user option 'flymake-diagnostic-format-alist'.
This provides fine-grained control over diagnostic formatting across
different contexts, allowing you to specify which components (origin,
code, message or one-liner message) appear in each output destination.

One of the problems with flymake is that its backends do crude filtering to separate the wheat from the chaff. But if you want to exclude very particular things, it’s often a bit of a chore, as you’re effectively forced to rewrite the filter routine to handle weird exceptions like never show warnings X, Y, and Z.

Dynamic column sizing in diagnostic listings.
The tabulated listings produced by 'flymake-show-buffer-diagnostics' and
'flymake-show-project-diagnostics' now automatically adjust their column
widths based on content, optimizing display space and readability.

New value 'auto' of user option 'flymake-indicator-type'.
This value (set by default) tries to use fringes if possible, otherwise
falls back to margins.

New user option 'elisp-flymake-byte-compile-executable'.
This allows customizing the Emacs executable used for Flymake byte
compilation in 'emacs-lisp-mode'.  This option should be set when editing
Lisp code which will run with a different Emacs version than the running
Emacs, such as code from an older or newer version of Emacs.  This will
provide more accurate warnings from byte compilation.

SQLite

Emacs has builtin support for SQLite, though it does require that you compile Emacs with it. Most distros seem to do so by default.

SQLite databases can now be opened in read-only mode.
The new optional argument READONLY of function 'sqlite-open' allows
opening an existing database only for reading.

'sqlite-open' now recognizes 'file://' URIs as well as file names.
'file://' URIs are supported by default.  In the unusual case that a
normal file name starts with "file:", you can disable the URI
recognition by calling 'sqlite-open' with the new optional argument
DISABLE-URI non-nil.

'sqlite-close' now does nothing if the connection is already closed.

GUD

GUD, or the Grand Unified Debugger, is a multi-window debugger for the likes of gdb, pdb and so on. It is very feature rich.

'pdb', 'perldb', and 'guiler' suggest debugging the current file via 'M-n'.
When starting these debuggers (e.g., 'pdb') while visiting a file,
pressing 'M-n' in the command prompt suggests a command line including
the file name, using the minibuffer's future history.

Calendar

Emacs’s M-x calendar is surprisingly useful and feature rich, with a laundry list of builtin calendaring features.

New command 'C-l' ('calendar-recenter').
This command recenters the month of the date at point.

Mouse wheel bindings for scrolling the calendar.
You can now use the mouse wheel to scroll the calendar by 3 months.
With the shift modifier, it scrolls by one month.  With the meta
modifier, it scrolls by one year.

Simpler key bindings for navigation in calendar by months and by years.
The month and year navigation key bindings 'M-}', 'M-{', 'C-x ]' and
'C-x [' now have the alternative keys '}', '{', ']' and '['.

Avoid modifying Calendar's user options.
The user options 'calendar-mark-holidays-flag' and
'calendar-mark-diary-entries-flag' are no longer modified when changing
the marking state in the calendar buffer.

New library for iCalendar data.
A new library has been added to Emacs for handling iCalendar (RFC 5545)
data.  The library is designed for reuse in other parts of Emacs and in
third-party packages.  Package authors can find the new library in the
Emacs distribution under "lisp/calendar/icalendar-*.el".

Most of the functions and variables in the older icalendar.el have been
marked obsolete and now suggest appropriate replacements from the new
library.  diary-icalendar.el provides replacements for the diary-related
features from icalendar.el; see below.

Diary

Diary - a diary that sort-of goes hand in hand with the calendar feature. It’s got a lot of esoteric features that warrants a deeper dive, to be honest. If you’re in the market for such a feature, do check out its (rather basic) info pages and associated calendaring features.

New user option 'diary-date-insertion-form'.
This user option determines how dates are inserted into the diary by
Lisp functions.  Its value is a pseudo-pattern of the same type as in
'diary-date-forms'.  It is used by 'diary-insert-entry' when inserting
entries from the calendar, or when importing them from other formats.

New library diary-icalendar.el.
This library reimplements features previously provided by icalendar.el:
import from iCalendar format to the diary, and export from the diary to
iCalendar.  It also adds the ability to include iCalendar files in the
diary and display and mark their contents in the calendar without
importing them to the diary file.  The library uses the new iCalendar
library (see above) and makes diary import and export more customizable.

New commands to display more months in the calendar.
'calendar-show-more-months' and 'calendar-show-fewer-months' display
more or fewer months in the calendar, respectively.  The calendar shows
at most 12 months and at least 3 months.

'calendar-scroll-left-three-months' and its variants are obsolete aliases.
Because the calendar can now display more than three months, commands
'calendar-scroll-left-three-months' and
'calendar-scroll-right-three-months' have been renamed to
'calendar-scroll-calendar-left' and 'calendar-scroll-calendar-right'.
The old names are kept for now as obsolete aliases.

Calc

One of two calculators in Emacs. This is the uber-advanced Computer Algebra System and reverse polish notation calculator bound to M-x calc. Well worth learning if you need a calculator. Every time I read about it or explore the manual, I learn new amazing things about it.

New user option 'calc-string-maximum-character'.
Previously, the 'calc-display-strings', 'string', and 'bstring'
functions only considered integer vectors whose elements are all in the
Latin-1 range 0-255.  This hard-coded maximum is replaced by
'calc-string-maximum-character', and setting it to a higher value allows
the display of matching vectors as Unicode strings.  The default value
is 0xFF or 255 to preserve the existing behavior.

New user option 'calc-inhibit-startup-message'.
If it is non-nil, inhibit Calc from printing its startup message.  The
default value is nil to preserve the existing behavior.

Time

M-x world-clock, M-x lunar-phases, etc.

New user option 'world-clock-sort-order'.
This option controls the order of timezone entries in the 'world-clock'.
By default, no sorting is done, and entries appear in the same order as
in 'world-clock-list'.  Any format understood by 'format-time-string'
can be used to specify a key for the sort order, which is updated upon
each refresh.  The sort direction can be controlled by using a cons cell
of a format string and a boolean.  Alternatively, a sorting function can
be provided directly.

New user option 'display-time-help-echo-format'.
This option controls the format of the help echo when hovering over the
time.

Fill

Fill region and its new counterpart in 31, the M-x unfill-paragraph.

New variable 'fill-region-as-paragraph-function'.
The new variable 'fill-region-as-paragraph-function' provides a way to
override how functions like 'fill-paragraph' and 'fill-region' fill
text.  Major modes can bind this variable to a function that fits their
needs.  It defaults to 'fill-region-as-paragraph-default'.

Newsticker

This is an RSS feed reader that is built into Emacs. I never really got on with it. I always felt like it had too many stateful things going on, and if you snuck up behind it and ran the wrong command, something always got wedged, and it’d end up in a weird doom loop.

If you love RSS, as I am sure you do, try the Elfeed package instead.

New user option 'newsticker-hide-old-feed-header'.
It controls whether to automatically hide the header of feeds whose
items are all old or obsolete in the plainview "*newsticker*" buffer.
This is only visually interesting if the content of those feeds are also
hidden (see 'newsticker-hide-old-items-in-newsticker-buffer' and
'newsticker-show-descriptions-of-new-items').

New commands to hide and show headers of old newsticker feeds.
The new commands 'newsticker-hide-old-feed-header' and
'newsticker-show-old-feed-header', bound to 'h h' and 's h',
respectively, hide and show the headers of feeds whose items are all old
or obsolete.

CPerl mode

Syntax of Perl up to version 5.42 is supported.
CPerl mode creates Imenu entries for ":writer" generated accessors and
recognizes the new builtin functions "all" and "any".
See https://perldoc.perl.org/5.42.0/perldelta for details.

Zone

M-x zone is Emacs’s screensaver. I do recommend turning it on, but only in an environment where your colleagues are likely to walk past your monitor and see your screen go completely postal.

Zone can scramble multiple windows across multiple frames; it may also
reorganize frames to be a single window.  As before, when a key or mouse
event occurs, all of the frames and windows are restored to their
original state.  This is controlled by three new user options which
control the use of frames and windows beyond the currently active ones.
It identifies suitable buffers for zoning out so that potentially
important buffer contents are not exposed.

Ordinarily, if you’re read this, you’d think what the heck, but… yeah, this is Zone alright.

New user option 'zone-delete-other-windows'.
When non-nil, the frame is made into a single full frame window to hold
the zoned buffer.  If all frames were to be used ('zone-all-frames' set
to non-nil), then all frames are converted to single window frames.

New user option 'zone-all-frames'.
When non-nil, Zone will appear on all visible frames.  While the buffer
scrambling will appear on each frame, it will be the same buffer so they
will all behave the same way.

New user option 'zone-all-windows-in-frame'.
When non-nil, the zoned buffer will be mapped to all of the windows
present on the frame.  If the option is nil, then only the selected
window will show the zoned buffer.  Note, however, that each window
holding the zoned buffer is showing the same zoned buffer.

New variable 'zone-ignored-buffers'.
This variable is a list of criteria for excluding a buffer from
consideration as the source of zoning.  The list has entries that are
tested against each buffer until a suitable one is found.  The criteria
can be a symbol whose name ends in "-mode" which excludes buffers that
are in a mode derived from the specified mode.  It may also be a
function-bound symbol or anonymous function (lambda expression) that is
called with a buffer that returns a non-nil value if it should not be
the Zone source.  Finally, an entry can also be a regular expression
that must not match the buffer's name.

Initially, the list excludes buffers in 'special-mode', in 'image-mode',
containing an encrypted file, is empty, is hidden, or is the "*scratch*"
buffer.  If it cannot locate any acceptable buffers, it will
begrudgingly use the "*scratch*" buffer.

Sometimes I wonder what prompts people to build out all this elaborate complexity for a screensaver that ostensibly exactly no one would ever really get to sit at and admire for any length of time. But that’s Emacs for you.

Abbrev mode

Abbrevs are little word auto corrections you can set up. See Correcting Typos and Misspellings with Abbrev.

You can now enable Abbrev mode by default using Easy Customization.
Customize the user option 'abbrev-mode' to non-nil to enable Abbrev mode
by default in all buffers.

Antlr mode

For writing language grammars for the ANTLR tool.

Variable 'antlr-tool-version' is no longer a user option.
It is now buffer-local and has the symbol 'antlr-v2', 'antlr-v3' or
'antlr-v4' as its value.  The value determines which of the tool
version-dependent customization options are used.  For example, the
command 'antlr-run-tool' uses the option 'antlr-v3-tool-command' (with
default value "java org.antlr.Tool") when 'antlr-tool-version' has the
value 'antlr-v3'.

'antlr-mode' now also works on ANTLR v3 or v4 grammars.
If the variable 'antlr-tool-version' is not set locally, e.g., by the
file's local variables specs, the command sets its local value to
'antlr-v2' if a keyword "class" or "header" appears at the beginning of
the source, or to 'antlr-v3' otherwise.

New 'antlr-v4-mode' is a derived mode of 'antlr-mode'.
It sets 'antlr-tool-version' to value 'antlr-v4', and is automatically
used for files with extension ".g4".

The variable 'antlr-language' is now used more generally.
The variable's value is a symbol which determines which of the
language-dependent customization options are used.  These options
influence font-locking and indentation commands.  Its value is usually
set according to the grammar option "language", see the default values
of 'antlr-v2-language-list', 'antlr-v3-language-list' and
'antlr-v4-language-list'.  This mode now supports C, Delphi, JavaScript,
ObjC, Python and Ruby, in addition to Java and C++.

New user option 'antlr-run-tool-on-buffer-file'.
The command 'antlr-run-tool' now usually runs on the file for the
current buffer.  Customize this user option to nil to get the previous
behavior back.

Hi Lock

Hi-Lock or “Highlighting” (see Highlighting by Word, Line and Regexp) is a cool feature that highlights stuff based on words, regexp, etc.

It’s called “lock” because font locking is how you syntax highlight, and hi locking is therefore the highlighter equivalent of that.

The active region is used for default values in more functions.
If an active region exists, the commands 'hi-lock-line-face-buffer' and
'hi-lock-face-phrase-buffer' now use its contents as their default
value.  Previously, only 'hi-lock-face-buffer' supported this.

Shadowfile

Obscure Emacs feature that maintains copies of files you edit in other places.

'shadow-info-buffer' and 'shadow-todo-buffer' now use ephemeral buffer names.

Display Battery mode

For laptop users or people with fantastically complex battery-backed desktops and servers.

UPower battery status can update automatically without polling.
On systems where the user option 'battery-status-function' is set to
'battery-upower', it is now possible to get battery status updates on
the mode line without polling for changes every
'battery-update-interval' seconds.  Setting this user option to nil
means the mode line will update only when the battery power state,
percentage, or presence in the bay changes.

Etags Regen mode

The tags table is no longer created during completion.
Previously, when there was no tags table loaded and the default
completion function was called, 'etags-regen-mode' ensured that tags
were created.  This has been disabled, and the new user option
'etags-regen-create-on-completion' can be used to enable it again.

Miscellaneous

'tooltip-mode' now shows tooltips on TTY frames after a delay.
Display of tooltips on text-only terminals now happens after
'tooltip-delay', as it already did on GUI terminals.  To get back the
old behavior, customize the value of 'tooltip-delay' to zero.

New user option 'follow-mode-prefix-key'.
This user option replaces 'follow-mode-prefix', which had to be set
before loading Follow mode.  This new option allows you to change the
prefix even after it was loaded, using 'customize-option' or 'setopt'.

cdl.el is now obsolete.
Use 'shell-command' and 'shell-command-on-region' instead.

echistory.el is now obsolete.

hashcash.el is now obsolete.
It is believed to no longer be useful as a method to fight spam.

kermit.el is now obsolete.

New user option 'ns-click-through' on Nextstep (GNUstep/Mac OS).
This controls whether activation clicks are passed through to Emacs
commands.  When nil, clicking on an inactive Emacs frame will only
activate it.  When t (the default), the click will both activate the
frame and be interpreted as a command.

New user option 'global-hl-line-buffers'.
This specifies the buffers in which 'global-hl-line-mode' should be
switched on.  The default is all buffers except the minibuffer, and
buffers that enable 'cursor-face-highlight-mode', like the
"*Completions*" buffer.

New value 'window' for the user option 'global-hl-line-sticky-flag'.
Unlike the value t that highlights the line containing point, it
highlights the line with the window's point.  Also it uses the new face
'hl-line-nonselected' for highlighting the line with the window's point
in non-selected windows.

New user option 'display-fill-column-indicator-warning'.
Customize it to a non-nil value to have the fill-column indicators
change their face if the current line exceeds the 'fill-column'.  The
new face 'display-fill-column-indicator-warning-face' is used to
highlight the fill-column indicators.  By default, this is disabled.

New function 'flash-face-bell-function'.
This function flashes a face briefly.
It is intended to be used in 'ring-bell-function'.

New function 'flash-echo-area-bell-function'.
This function flashes the current frame's echo area briefly.
It is intended to be used in 'ring-bell-function'.

New user option 'flash-face-faces'.
This option tells 'flash-face-bell-function' which faces should flash.

New user option 'flash-face-attributes'.
This option tells 'flash-face-bell-function' and
'flash-echo-area-bell-function' which face attributes should be used
to flash.

'face-all-attributes' now accepts an optional argument INHERIT.
It has the same meaning as the INHERIT argument to 'face-attribute',
which already takes this argument for a single attribute.  This is
useful when you want the face attributes to be absolute and not
'unspecified'.

New user option 'ffap-prefer-remote-file'.
If non-nil, FFAP always finds remote files in buffers with remote
'default-directory'.  If nil, FFAP finds local files first for absolute
file names in those buffers.  The default is nil.

New theme 'newcomers-presets'.
This new theme configures user options and minor modes that might
interest new users, but would otherwise be too invasive to enable by
default.  It is basically a set of alternative defaults.  (An Emacs
theme is a generic collection of settings, and need not affect Emacs's
appearance.)  See the Info node "(emacs) Newcomers Theme" for more
information.

Shame this got buried all the way at the bottom. This is a subject that has been debated to death, again and again, on mailing lists and elsewhere.

Should Emacs have better defaults? Which of course is a loaded question because it does change, and it has absolutely improved its defaults. Fire up a copy of Emacs 21 and Emacs 31 without mods and daily drive them for a day and see what I mean by that.

But anyway. Yes, this is a good thing. It does not affect Emacs veterans (though I’m sure curmudgeons will find a way of claiming it does) and newbies can activate a mode that will give them slightly saner defaults out of the box.

So what does it do then? It enables a bunch of incredibly conservative features that, honestly, should be the default already. Like electric pair mode (auto-insert closing braces and quotes, that sort of thing); saving the history of completions you’ve made; display line numbers and enable flymake. And a smattering of not terribly interesting long tail of changes most people (certainly not newbies) would have much of an opinion about.

This speaks to the conservatism of the maintainers who made collectively arrived at these decisions, or perhaps… the absence of changes you can reasonably make to make a newbie’s life easier.

My view is on the latter. Emacs is already in a pretty good place, but Emacs is an advanced tool. No amount of turning stuff on or off will ever change that.

'report-emacs-bug' now checks whether the bug report is about Org.
The command 'report-emacs-bug' looks in the report text for symbols that
indicate problems in Org, and if found, will ask whether the bug report
is actually about Org (in which case users should use the Org-specific
command for reporting bugs).

The elint.el package is now obsolete.
Use the byte-compiler instead; it provides more and more useful warnings.

New Modes and Packages in Emacs 31.1

New major mode 'icalendar-mode'.
A major mode for displaying and editing iCalendar (RFC 5545) data.  This
mode handles line unfolding and fontification, including highlighting
syntax errors in invalid data.

New minor mode 'delete-trailing-whitespace-mode'.
A simple buffer-local mode that runs 'delete-trailing-whitespace'
before saving the buffer.

A minor mode that does something a lot of people end up hand-building themselves.

New major mode 'conf-npmrc-mode'.
A major mode based on 'conf-mode' for editing ".npmrc" files.

New major modes based on the tree-sitter library

New major mode 'mhtml-ts-mode'.
An optional major mode based on the tree-sitter library for editing HTML
files.  This mode handles indentation, fontification, and commenting for
embedded JavaScript and CSS.

New major mode 'go-work-ts-mode'.
A major mode based on the tree-sitter library for editing "go.work"
files.  If tree-sitter is properly set-up by the user, it can be
enabled for files named "go.work".

New package 'lua-mode'.
The 'lua-mode' package from NonGNU ELPA is now included in Emacs.

New library 'timeout'.
This library provides functions to throttle or debounce Emacs Lisp
functions.  This is useful for corralling overeager code that is slow
and blocks Emacs, or does not provide ways to limit how often it runs.

New mode 'system-taskbar-mode'.
This is a global minor mode and companion functions that integrate Emacs
with system GUI taskbars (also called docks or launchers or something
similar) to display a taskbar icon badge overlay, a progress bar report
overlay, and alerts that an Emacs session needs attention, often by
flashing or bouncing the Emacs application icon.  Supported on GNU/Linux
via D-Bus, macOS/GNUstep 10.5+ and MS-Windows 7+.

On GNU/Linux systems, shell extensions or similar helpers such as
"dash-to-dock" may be required.  See
<https://extensions.gnome.org/extension/307/dash-to-dock/> and
<https://wiki.ubuntu.com/Unity/LauncherAPI>.

Hey that’s pretty neat. I don’t use a WM where that makes a difference to me, I don’t think (I use Hyprland) but I’d love to hear from people who do use it, and if it helps.

New package 'system-sleep'.
This package provides platform-neutral interfaces to block your system
from entering idle sleep and a hook to process pre-sleep and post-wake
events.  You can use this to avoid the system entering an idle sleep
state and interrupting a long-running process due to a lack of user
activity.  The sleep event hook can, for example, close external
connections or serial ports before sleeping, and re-establish them when
the system wakes up.

Supported on GNU/Linux via D-Bus (sleep blocking and sleep events
require the org.freedesktop.login1 service, display sleep blocking
requires org.freedesktop.Screensaver service), macOS (sleep/display
blocking requires version 10.9 or later, sleep events are supported on
all versions), MS-Windows (sleep blocking is supported on all versions,
sleep events require Windows 8 or later).

Incompatible Lisp Changes in Emacs 31.1

Boundaries of 'cursor-sensor-functions' now obey stickiness.
'cursor-sensor-mode' now uses 'get-pos-property' to decide whether a
boundary is considered to be inside or outside.

This means that by default, the boundaries have changed: the end
position of a stretch of a 'cursor-sensor-functions' text property used
to be considered outside of the stretch whereas it is now considered to
be inside.  You can recover the previous behavior by controlling the
stickiness, for example with a call like:

    (add-text-properties BEG END
                         '(cursor-sensor-functions (MY-FUNCTION)
                           rear-nonsticky (cursor-sensor-functions)))

'makunbound' on a variable alias undoes the alias.
Previously, it had the effect of applying the 'makunbound' to the target
of the alias (which can fail for some builtin variables).

'FOO-ts-mode-indent-offset' renamed to 'FOO-ts-indent-offset'.
When the new TS modes were introduced, a mistake was made where those
modes used 'FOO-mode-indent-offset' instead of the conventional
'FOO-indent-offset'.  The following are the new names:
'toml-ts-indent-offset', 'mhtml-ts-js-css-indent-offset',
'html-ts-indent-offset', 'typescript-ts-indent-offset',
'php-ts-indent-offset', 'php-ts-html-indent-offset',
'json-ts-indent-offset', 'java-ts-indent-offset',
'go-ts-indent-offset', 'csharp-ts-indent-offset',
'cmake-ts-indent-offset', 'c-ts-indent-offset'.

String mutation has been restricted further.
'aset' on unibyte strings now requires the new character to be a single
byte (0-255).  On multibyte strings the new character and the character
being replaced must both be ASCII (0-127).

These rules ensure that mutation will never transform a unibyte string
to multibyte, and that the size of a string in bytes (as reported by
'string-bytes') never changes.  They also allow strings to be
represented more efficiently in the future.

Other functions that use 'aset' to modify string data, such as
'subst-char-in-string' with a non-nil INPLACE argument, will signal an
error if called with arguments that would violate these rules.

More program constants are combined by the compiler.
The compiler now unifies more constants that are 'equal' for better code
generation.  This does not affect correct programs but may expose some
coding mistakes.  For example,

    (eq (cdr '(1 2 3)) '(2 3))

may return either nil or t.

Nested backquotes are no longer supported in Pcase patterns.

The obsolete variable 'redisplay-dont-pause' has been removed.

The 'rx' category name 'chinese-two-byte' must now be spelled correctly.
An old alternative name (without the first 'e') has been removed.

'text-property-default-nonsticky' is now buffer-local.
This variable now becomes buffer-local when set.  Use 'setq-default' in
the (unlikely) case you want to change the global value.

All the digit characters now have the 'digit' category.
All the characters whose Unicode general-category is Nd now have the
'digit' category, whose mnemonic is '6'.  This includes both ASCII and
non-ASCII digit characters.

All the symbol characters now have the 'symbol' category.
All the characters that belong to the 'symbol' script (according to
'char-script-table') now have the 'symbol' category, whose mnemonic is
'5' (it looks like an 'S').

Some libraries obsolete since Emacs 24.4 and 24.5 have been removed:
cc-compat.el, info-edit.el, meese.el, otodo-mode.el, rcompile.el,
sup-mouse.el, terminal.el, vi.el, vip.el, ws-mode.el, and yow.el.

'if-let' and 'when-let' are now obsolete.
Use 'if-let*', 'when-let*' and 'and-let*' instead.

This effectively obsoletes the old '(if-let (SYMBOL SOMETHING) ...)'
single binding syntax, which we'd kept only for backwards compatibility.

Sigh.. more unnecessary obsolescence churn, all because of some chicanery in a few extreme cases where the macros didn’t do what people thought it did.

The Eshell 'pwd' command now expands the directory name on all systems.
This ensures that user directories are properly expanded to their full
name.  Previously, Eshell only did this for MS-Windows systems.  To
restore the old behavior, you can set 'eshell-pwd-convert-function' to
'identity'.

The rx 'eval' form now uses the current Lisp dialect for evaluation.
Previously, its argument was always evaluated using dynamic binding.

Unused block comment variables have been removed.
The unused variables 'block-comment-start' and 'block-comment-end',
which never actually had any effect when set by major modes, have been
removed.

'delete-frame' now needs a non-nil FORCE to delete the daemon frame.
The initial terminal frame of an Emacs process running as daemon can be
deleted via 'delete-frame' if and only if its optional FORCE argument is
non-nil.

'date-to-time' no longer accepts malformed times with time zone like "EDT".
Time strings like "2025-06-04T13:21:00 EDT" are not in valid ISO 8601
time format, and 'date-to-time' now signals an error for them.  Use a
numerical time-zone specification, like "2025-06-04T13:21:00-0400",
instead, which gives the time offset as +/-hh or +/-hh:mm.  A designator
"Z" for UTC time is also supported.  Less formal space-separated time
formats, like "2025-06-04 13:21:00 EDT", without the ISO 8601 "T"
separator, are also supported.

The obsolete variable 'load-convert-to-unibyte' has been removed.

The experimental variable 'binary-as-unsigned' has been removed.
Instead of '(let ((binary-as-unsigned t)) (format "%x" N))' you can use
'(format "%x" (logand N MASK))' where MASK is for the desired word size,
e.g., #x3fffffffffffffff for typical Emacs fixnums.

The 'exec-path' variable now uses same default PATH as other programs.
That is, if the PATH environment variable is unset or empty, 'exec-path'
now acts as if PATH is the system default, which is "/bin:/usr/bin"
on GNU/Linux systems.

New variable 'tty-cursor-movement-use-TAB-BS'.
The display optimization where the combination 'TAB' characters +
'BACKSPACE' is used to move to a position on a TTY frame is now disabled
by default and controlled by this variable; it can be set to non-nil
to keep the old behavior.  This change is to accommodate screen
readers.

'next-completion' and 'previous-completion' now use 'completions-format'.
Previously, these commands only took horizontal format into account;
now, they call either '{next,previous}-line-completion' or the new
commands '{next,previous}-column-completion', depending on the value of
'completions-format'.  The latter two commands improve and extend the
previous implementations of '{next,previous}-completion', which better
reflect that they only take the (default) horizontal completions format
into account.  Any external code using '{next,previous}-completion' that
assumes the previous implementation must be adjusted accordingly; see
'minibuffer-next-completion' for an example of such an adjustment in
Emacs core.

A thread's current buffer can now be killed.
We introduce a new attribute for threads called "buffer disposition".
See the new argument in 'make-thread' as well as the
'thread-buffer-disposition' and 'thread-set-buffer-disposition' functions.
The default value allows the thread's current buffer to be killed by another
thread.  This does not apply to the main thread's buffer.

Defining or modifying a face so that it inherits from itself signals error.
Calling any function that defines or modifies a face in a way that
causes cyclical inheritance (i.e., the face inherits from itself, either
directly or indirectly) now signals an error.  Previously, Lisp programs
could get away with this, and the problem would either be detected at
display time or even cause Emacs to hang trying to display such a face.
Affected APIs include 'defface', 'set-face-attribute', their callers,
and other similar functions.

Original behavior of 'overlays-in' and 'overlays-at' has been restored.
Before Emacs 28.1, the list of overlays returned by these two functions
included overlays outside of the current narrowing of the buffer, and
there wasn't a special exception for including empty overlays at end of
accessible portion of the buffer.  This behavior has been restored, and
the special behavior for empty overlays is again reserved only to the
actual end of buffer, disregarding narrowing.  As result,
'remove-overlays' can now again remove overlays outside of the
narrowing, as it did before Emacs 28.1.

'help-setup-xref' now re-enables the major mode of the Help buffer.
As a result, in many cases the buffer will be read-only afterwards.
This should not cause any trouble as long as the actual buffer
modification takes place inside 'with-help-window' or
'with-output-to-temp-buffer' after the call to 'help-setup-xref'.

Xref commands don't automatically suggest visiting a tags table anymore.
When no tags file is loaded, symbol completion now just won't provide
any suggestions.  Thus, so the 'M-?' command now works without a tags
table.  And the 'M-.' command will show a message describing the several
built-in options that will provide an Xref backend when used.

Calling 'debug' in batch sessions no longer kills Emacs.
If you want Emacs to exit, your program will now have to call
'kill-emacs' explicitly.

Lisp Changes in Emacs 31.1

The API to manipulate error descriptors has been improved.
There are new functions: 'error-type-p', 'error-type',
'error-has-type-p', and 'error-slot-value'.  You can now say '(signal
err)' instead of '(signal (car err) (cdr err))', which is not only more
concise, but also preserves the equality (under 'eq') of the error
descriptor.

'secure-hash' now supports generating SHA-3 message digests.
The list returned by 'secure-hash-algorithms' now contains the symbols
'sha3-224', 'sha3-256', 'sha3-384', and 'sha3-512'.  These symbols can
be used as the ALGORITHM argument of 'secure-hash' to generate SHA-3
hashes.

New function 'garbage-collect-heapsize'.
Same as 'garbage-collect' but just returns the info from the last GC
without performing a collection.

Improve 'replace-region-contents' to accept more forms of sources.
It has been moved from subr-x.el to editfns.c.  You can now directly
pass it a string or a buffer rather than a function.  Passing a function
is now deprecated.

New function 'char-displayable-on-frame-p'.
'char-displayable-on-frame-p' returns non-nil if Emacs ought to be able
to display its char argument on a given frame.  This new function,
unlike 'char-displayable-p', does not check whether the character can be
encoded by the underlying terminal.

New function 'frame-initial-p'.
This predicate returns non-nil if a given frame or terminal is or holds,
respectively, the initial text frame that is used internally during
daemon mode, batch mode, and the early stages of startup.  Interactive
and graphical programs, for instance, can use this predicate to avoid
operating on the initial frame, which is never displayed.

New macros 'static-when' and 'static-unless'.
Like 'static-if', these macros evaluate their condition at
macro-expansion time and are useful for writing code that can work
across different Emacs versions.

New feature to speed up repeated lookup of Lisp files in 'load-path'.
If the new variable 'load-path-filter-function' is set to the new
function 'load-path-filter-cache-directory-files', calling 'load' will
cache the directories it scans and their files, and the following
lookups should be faster.

'let-alist' supports indexing into lists.
The macro 'let-alist' now interprets symbols containing numbers as list
indices.  For example, '.key.0' looks up 'key' in the alist and then
returns its first element.

Lexical binding

You can change the default value of 'lexical-binding'.
While the default is still the use of dynamic binding dialect of Emacs
Lisp in those places that don't explicitly set 'lexical-binding', you
can change it globally with:

    (set-default-toplevel-value 'lexical-binding t)

But don’t do that. Lexical binding is great; it’s the future; we have dynamic binding forever for special forms like defvar so most things just work as they should. But don’t go enabling this. Let package authors update their code in their own time.

Loading a file displays a warning if there is no 'lexical-binding' cookie.

Files loaded from '-x' and '--script' now use lexical binding.
If you don't have time to adapt your script's code to the lexical
binding dialect (see "(elisp) Converting to Lexical Binding"), you can
wrap your code in:

    #!/usr/bin/env -S emacs --batch --script
    (eval
     '(progn
        YOUR CODE HERE))

Huh I thought they already used lexical binding.

New function 'set-local'.
This is the buffer-local equivalent of the function 'set'.

New macro 'setopt-local'.
This is the buffer-local version of 'setopt' for user options rather
than plain variables, and uses 'custom-set'/'set-local' to set variable
values.  A new argument, BUFFER-LOCAL, is passed to 'custom-set'
functions to indicate the buffer-local context.

New macros 'incf' and 'decf'.
They increment or decrement the value stored in a variable (a symbol),
or in a generalized variable.

New functions 'plusp' and 'minusp'.
They return non-nil if a number is positive or negative, respectively,
and signal an error if they are given a non-number.

New functions 'oddp' and 'evenp'.
They return non-nil if an integer is odd or even, respectively, and
signal an error if they are given a non-integer.

New functions 'drop-while' and 'take-while'.
These work like 'drop' and 'take' but use a predicate instead of
counting.

New function 'all' and function alias 'any'.
These return non-nil for lists where all and any elements, respectively,
satisfy a given predicate.

'equal' now compares circular lists without signalling an error.
Comparing very deeply nested objects will still fail, but 'equal'
will no longer signal the 'circular-list' error.

The 'defvar-local' macro's second argument is now optional.
This means that you can now call it with just one argument, like
'defvar', to declare a variable both special and buffer-local.

The rx atom 'any' is obsolete and usage emits warnings.
When used as an atom, 'any' is an old alias for 'not-newline' but is
often mistakenly used where 'anychar' was intended.  Note that the
construct '(any ...)' is unrelated and not obsolete.

ERT

ERT is Emacs’s elisp test framework.

Some experimental ERT macros are now considered stable.
The following macros, previously only available in the experimental
'ert-x' module, are now considered stable and have been moved to 'ert':

- 'ert-with-test-buffer'
- 'ert-with-buffer-selected'
- 'ert-with-buffer-renamed'

See "(ert) Helper Functions" node in the ERT manual for more information.

New function 'ert-play-keys'.
Previously, 'ert-simulate-keys' could be used for sending keys to input
functions such as 'read-from-minibuffer', but not for other interactive
input such as starting key-mapped commands.

Show executed tests from erts files via the ERT results buffer.
For tests that call 'ert-test-erts-file', the ERT results buffer now
allows you to list the tests defined in the referenced erts files that
have been executed by the test at point.  See Info node "(ert) Running
Tests Interactively" for more information.

Time & Date

'seconds-to-string' supports new formatting options.
Optional arguments are provided to produce human-readable time-duration
strings in a variety of formats, for example "6 months 3 weeks" or "5m
52.5s".

New function 'hash-table-contains-p'.
This function returns non-nil if a given key is present in a hash table.

The function 'purecopy' is now an obsolete alias for 'identity'.

New function 'native-compile-directory'.
This function natively compiles all Lisp files in a directory and in its
sub-directories, recursively, excluding those already natively compiled.

New function 'color-blend'.
This function takes two RGB lists and optional ALPHA and returns an RGB
list whose elements are blended in linear space proportional to ALPHA.

New function 'dom-inner-text'.
This function gets all the text within a DOM node recursively, returning
it as a concatenated string.  It replaces the now-obsolete functions
'dom-text' and 'dom-texts'.

The obsolete face attribute ':reverse-video' has been removed.
Use ':inverse-video' instead.

D-Bus

D-Bus is a generic mechanism for inter-application and app-OS communication on Linux.

Support interactive D-Bus authorization.
A new ':authorizable t' parameter has been added to 'dbus-call-method'
and 'dbus-call-method-asynchronously' to allow the user to interactively
authorize the invoked D-Bus method (for example via polkit).

Support D-Bus file descriptor manipulation.
A new ':keep-fd' parameter has been added to 'dbus-call-method' and
'dbus-call-method-asynchronously' to instruct D-Bus to keep a file
descriptor, which has been returned by a method call, internally.  The
functions 'dbus--fd-open', 'dbus--fd-close' and 'dbus--registered-fds'
implement managing these file descriptors.  See the Info node "(dbus)
File Descriptors" for details.

The customization group 'wp' has been removed.
It has been obsolete since Emacs 26.1.  Use the group 'text' instead.

New optional BUFFER argument for 'string-pixel-width'.
If supplied, 'string-pixel-width' will use any face remappings from
BUFFER when computing the string's width.

New function 'truncate-string-pixelwise'.
This function truncates a string to the specified maximum number of
pixels rather than by characters, as in 'truncate-string-to-width', and
respects face remappings if BUFFER is specified.  You can also specify
an optional ellipsis string to append, similar to
'truncate-string-to-width'.

New macro 'with-work-buffer'.
This macro is similar to the already existing macro 'with-temp-buffer',
except that it does not allocate a new temporary buffer on each call,
but tries to reuse those previously allocated (up to a number defined by
the new variable 'work-buffer-limit', which defaults to 10).

'date-to-time' now defaults to local time.
The function now assumes local time instead of Universal Time when
its argument lacks explicit time zone information.  This has been the
de-facto behavior since Emacs 24 although documentation said otherwise.
Also, the fallback on 'timezone-make-date-arpa-standard' has been
removed because its supported date styles can be handled by
'parse-time-string'.  To restore the previously documented behavior,
specify "+0000" or "Z" as the time zone in the argument.

The 'min-width' property is now supported for overlays as well.
This 'display' property was previously supported only as text property.
Now overlays can also have this property, with the same effect for the
text covered by the overlay.

New function 'remove-display-text-property'.
This function removes a display property from the specified region of
text, preserving any other display properties already set for that
region.

New macro 'cond*'.
The new macro 'cond*' is an alternative to 'cond' and 'pcase'.
Like them, it can be used to define several clauses, each one with its
own condition; the first clause that matches will cause its body to be
evaluated.
'cond*' can use Pcase's pattern matching syntax and also provides
another pattern matching syntax that is different from that of 'pcase',
which some users might find less cryptic.
See the Info node "(elisp) cond* Macro" for details.

I’m not going to get into if we need or want cond*, but I do feel we need a better cond — but cond* is just a far more complex, in my opinion, way of doing something pcase can already do well.

New function 'shell-command-do-open'.
This lets a Lisp program access the core functionality of the
'dired-do-open' command.  It opens a file or files using an external
program, choosing the program according to the operating system's
conventions.

'make-vtable' can create an empty vtable.
It is now possible to create a vtable without data, by leaving the
':objects' list empty, or by providing an ':objects-function' that
(initially) produces no data.  In such a case, it is necessary to
provide a ':columns' spec, so that the number of columns and their
widths can be determined.  Column widths can be set explicitly, or they
will be calculated based on the window width.

New symbol property 'repeat-continue' for 'repeat-mode'.
A command with the 'repeat-continue' symbol property, which can be a
list of keymaps or t, will continue an already active repeating sequence
for a keymap in that list (resp. all keymaps).  The new property does
not affect whether the command starts a repeating sequence, which
remains governed by the 'repeat-map' property.  'defvar-keymap' supports
a new keyword ':continue', a list of commands, and adds the keymap to
the 'repeat-continue' property of each command in that list.  The
'use-package' and 'bind-keys' macros support a similar keyword
':continue-only'.

New function 'completion-table-with-metadata'.
It offers a more concise way to create a completion table with metadata.

'all-completions' and 'unintern' no longer support old calling conventions.

New symbol property 'find-function-type-alist'.
Used by 'find-function' and similar commands.  Macros that define an
object in a way that makes it hard to associate the object's name with
the macro call site defining the object can add an entry to the property
'find-function-type-alist' on the object's name to provide information
for finding the definition.

The new convenience function 'find-function-update-type-alist' offers a
concise way to update a symbol's 'find-function-type-alist' property.

New function variable 'comment-setup-function' for multi-language modes.
It can set comment-related variables such as 'comment-start' depending
on the language under point.

Required for any language that embed other languages. So mostly of use for tree-sitter major modes or stuff like the web-mode package.

'inhibit-message' can now inhibit clearing of the echo area.
Binding 'inhibit-message' to a non-nil value will now suppress both
the display of messages and the clearing of the echo area, such as
caused by calling 'message' with a nil argument.

'minibuffer-message' no longer blocks while displaying message.
'minibuffer-message' now uses a timer to clear the message printed to
the minibuffer, instead of waiting with 'sit-for' and then clearing it.
This makes 'minibuffer-message' usable in Lisp programs which want to
print a message and then continue to perform work.

Special Events

New primitive 'insert-special-event'.
This function inserts the special EVENT into the input event queue.

New event type 'sleep-event'.
This event is sent when the device running Emacs enters or leaves the
sleep state.

Function aliases obsolete since Emacs 23.2 have been removed:
'advertised-undo', 'advertised-widget-backward', and
'dired-advertised-find-file'.

New functions to get and set top-level buffer-local values.
'buffer-local-toplevel-value' and 'set-buffer-local-toplevel-value' get
and set the top-level buffer-local value of a variable.  A top-level
value is the one that variable has outside of any let-bindings.

New function 'exec-suffixes'.
This function by default returns the value of the corresponding user
option, but can optionally return the equivalent of 'exec-suffixes' from
a remote host.  It must be used in conjunction with the function
'exec-path'.

'read-directory-name' now accepts an optional PREDICATE argument.

JSON parse error line and column are now obsolete.
The column number is no longer available; the line number will be
removed in the next release of Emacs.

'defvar-keymap' can now take a ':prefix t' option.
This is an abbreviation for using the name of the keymap as the prefix
command name.  E.g., '(defvar-keymap foo-map :prefix t)' is equivalent
to '(defvar-keymap foo-map :prefix 'foo-map)'.

New 'R' code letter for 'interactive' forms.
This specifies the beginning and end of an active region, and nil twice
if the region is inactive.  The interactive specification

    (interactive "R")

is equivalent to

    (interactive (list (use-region-beginning) (use-region-end)))

Toolkit

The Emacs PGTK toolkit respects dark and light modes.
Emacs when built with the pure GTK toolkit now respects desktop dark and
light modes for drawing the GTK toolbar and widgets, automatically
toggling between them.

That’s lovely for people who love toggling between it and want their OS to govern this.

'toolkit-theme-set-functions' called when the toolkit theme is set for Emacs.
When the theme is set on PGTK, Android, or MS-Windows systems,
'toolkit-theme-set-functions' is called.  The result is stored in the
variable 'toolkit-theme' as either symbol 'dark' or 'light', but may be
extended to encompass other toolkit-specific symbols in the future.

Progress reporter context.
'make-progress-reporter' now accepts the optional argument CONTEXT,
which if it is the symbol 'async', inhibits updates in the echo area
when it is busy.  This is useful, for example, if you want to monitor
progress of an inherently asynchronous command such as 'compile'.

Binary format specifications '%b' and '%B' added.
These produce the binary representation of a number.  '%#b' and '%#B'
prefix the bits with '0b' and '0B', respectively.

'pp-eval-expression' can now insert results into the current buffer.
With a prefix argument, 'pp-eval-expression' inserts the result into the
current buffer, just like 'eval-expression' already did.

New function 'multiple-command-partition-arguments'.
This function partitions a list of command arguments that might be
arbitrarily long.  It can be used in cases in which it is known to be
safe to run the command multiple times on subsequent partitions of the
list of arguments.  The variable 'command-line-max-length' controls the
partitioning.

New function 'ensure-proper-list'.
This function is a variation on 'ensure-list' that checks if an object
is a proper list, in which case the list will be returned as is,
otherwise the function will return the object wrapped in a singleton
list.

In batch mode, 'C-c' (i.e. SIGINT) can either 'quit' or kill Emacs.
By default it kills Emacs, as before, but 'kill-emacs-on-sigint'
can be set to nil to change that.
The response to SIGINT in interactive sessions is unaffected,
e.g., in a normal GUI session it still kills Emacs whereas in a terminal
it causes 'quit' since it is used for 'C-g'.

New ':interactive-only' way to add an advice.
While it is marginally more efficient than ':after' or ':before',
the main purpose is to make the intention more obvious when the advice
modifies only the interactive form and not the actual behavior
of the function.

Changes in Emacs 31.1 on Non-Free Operating Systems

Support macOS Accessibility Zoom focus tracking.
This is an important change for visually-impaired users.  If macOS
Accessibility Zoom is enabled via (System Settings, Accessibility,
Zoom...) with keyboard focus tracking (Advanced...), Zoom is informed
of updated cursor positions during each redisplay cycle.

New macOS function 'ns-process-is-accessibility-trusted'.
This function returns t if the macOS Accessibility Framework trusts
Emacs.  This is a necessary condition for Accessibility Zoom and other
accessibility features.  Enable Emacs via (System Settings, Privacy &
Security, Accessibility...) and add the Emacs.app installed directory to
the enabled application list.

Process execution has been optimized on Android.
The run-time performance of subprocesses on recent Android releases,
where a userspace executable loader is required, has been optimized on
systems featuring Linux 3.5.0 and above.

It is now possible to read GUI events from non-main Lisp threads on Android.
Put differently, this enables input events to be read and recursive
editing sessions to be started from non-main threads.  The only platform
where this remains unsupported is Nextstep (GNUstep or macOS).

'desktop-restore-frames' has been disabled by default on Android systems.
Restrictions imposed on clients by the window manager on these systems
are too prohibitive and don't allow restoring frame configurations.
(For the same reason many window management facilities are also not
implemented by Emacs.)

Emacs responds to runtime display configuration changes on Android.
The upshot of this is that Emacs will adapt to display resolution /
layout changes applied while an Emacs session is active, which is
possible on some recently released devices.

'NSSpeechRecognitionUsageDescription' now included in "Info.plist" (macOS).
Should Emacs (or any built-in shell) invoke a process using macOS speech
recognition APIs, the relevant permission dialog is now displayed, thus
allowing Emacs users access to speech recognition utilities.

Note: Accepting this permission allows the use of system APIs, which may
send user data to Apple's speech recognition servers.

Re-introduced dictation, lost in Emacs 30 (macOS).
We lost macOS dictation in Emacs 30 when migrating to NSTextInputClient.
We have now implemented 'selectedRange' in 'nsterm.m' to enable it in
the new subsystem.  You may notice a slight change in dictation UI
provided by macOS.

On Mac OS X, stipples now render with color.

Emacs on MS-Windows now supports GUI dialogs and message boxes better.
In particular, it is now possible to show text with embedded newlines in
a dialog popped by 'message-box'.  This is supported on Windows Vista
and later versions.

Emacs on MS-Windows now supports drag-n-drop of text into a buffer.
This is in addition to drag-n-drop of files, which was already
supported.  As on X, the user options 'dnd-scroll-margin' and
'dnd-indicate-insertion-point' can be used to customize the process.

Emacs on MS-Windows now supports color fonts.
On Windows 8.1 and later versions, Emacs now uses DirectWrite to draw
text, which supports color fonts.  This can be disabled by setting the
variable 'w32-inhibit-dwrite' to t.  Also see 'w32-dwrite-available' and
'w32-dwrite-reinit' to check availability and to configure the
DirectWrite rendering parameters.

To show color Emojis in Emacs, customize the default fontset to use a
color Emoji font installed on your system for the 'emoji' script.

Emacs on MS-Windows now supports 'yank-media'.
This command inserts clipboard data of different formats into the
current buffer, if the major mode supports it.

Emacs on MS-Windows now supports up to 1024 sub-processes.
Changes in implementation of monitoring sub-processes allow Emacs on
MS-Windows to start up to 1024 sub-processes, similar to GNU/Linux and
other free systems.

Images on MS-Windows now support the ':transform-smoothing' flag.
Transformed images are smoothed using the bilinear interpolation by
means of the GDI+ library.

Emacs on MS-Windows is now capable of exporting frame screenshots to files.
The new primitive 'w32-export-frame' can be used to export a screenshot
of a specified frame to an image file in one of the supported image
formats, such as JPEG or PNG.

Emacs on MS-Windows now supports the ':data' keyword for 'play-sound'.
In addition to ':file FILE' for playing a sound from a file, ':data
DATA' can now be used to play a sound from memory.

New primitive 'w32-sound-volume'.
This primitive allows getting and setting the volume of the system's
default audio device (or the "optimal device", if there are several
devices).

The MS-DOS port of Emacs now supports more recent releases of GCC and Binutils.
Accordingly, we have revised our recommendations for a suitable DJGPP
toolchain to GCC 14.2.0 and Binutils 2.35.1 in lieu of GCC 3.4.x and
Binutils 2.26.

Windows Terminal can now display 256 and 24-bit RGB color.
Previously, terminal sessions on Windows supported display of 16 colors.
There is now support for 8-bit (256 color) and 24-bit RGB (true color).
The new mechanism will be enabled automatically when supported.
It defaults to 24-bit RGB color, but can be set to 8, 16, '8bit', or
'24bit' by passing the '--color' flag or setting the 'tty-color-mode'
frame parameter.  Use of the new mechanism is controlled by an internal
variable that can be set and inspected via the functions
'w32-use-virtual-terminal' and 'w32-use-virtual-terminal-p'
(respectively).  See the manual entry "(emacs) Windows Misc" for more
details.