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GNU Emacs NEWS -- history of user-visible changes.
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Copyright (C) 2017-2018 Free Software Foundation, Inc.
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See the end of the file for license conditions.
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Please send Emacs bug reports to 'bug-gnu-emacs@gnu.org'.
If possible, use 'M-x report-emacs-bug'.
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This file is about changes in Emacs version 27.
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See file HISTORY for a list of GNU Emacs versions and release dates.
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See files NEWS.26, NEWS.25, ..., NEWS.18, and NEWS.1-17 for changes
in older Emacs versions.
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You can narrow news to a specific version by calling 'view-emacs-news'
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with a prefix argument or by typing 'C-u C-h C-n'.
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Temporary note:
+++ indicates that all necessary documentation updates are complete.
    (This means all relevant manuals in doc/ AND lisp doc-strings.)
--- means no change in the manuals is needed.
When you add a new item, use the appropriate mark if you are sure it applies,
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24

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* Installation Changes in Emacs 27.1
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** Emacs now uses GMP, the GNU Multiple Precision library.
By default, if 'configure' does not find a suitable libgmp, it
arranges for the included mini-gmp library to be built and used.
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The new 'configure' option '--without-libgmp' uses mini-gmp even if a
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suitable libgmp is available.
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** The new configure option '--with-json' adds support for JSON using
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the Jansson library.  It is on by default; use './configure
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--with-json=no' to build without Jansson support.  The new JSON
functions 'json-serialize', 'json-insert', 'json-parse-string', and
'json-parse-buffer' are typically much faster than their Lisp
counterparts from json.el.

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** The etags program now uses the C library's regular expression matcher
when possible, and a compatible regex substitute otherwise.  This will
let developers maintain Emacs's own regex code without having to also
support other programs.  The new configure option '--without-included-regex'
forces etags to use the C library's regex matcher even if the regex
substitute ordinarily would be used to work around compatibility problems.

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** Emacs has been ported to the '-fcheck-pointer-bounds' option of GCC.
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This causes Emacs to check bounds of some arrays addressed by its
internal pointers, which can be helpful when debugging the Emacs
interpreter or modules that it uses.  If your platform supports it you
can enable it when configuring, e.g., './configure CFLAGS="-g3 -O2
-mmpx -fcheck-pointer-bounds"' on Intel MPX platforms.

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** Emacs now normally uses a C pointer type instead of a C integer
type to implement Lisp_Object, which is the fundamental machine word
type internal to the Emacs Lisp interpreter.  This change aims to
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catch typos and supports '-fcheck-pointer-bounds'.  The 'configure'
option '--enable-check-lisp-object-type' is therefore no longer as
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useful and so is no longer enabled by default in developer builds,
to reduce differences between developer and production builds.

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** Ibuffer

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---
*** All mode filters can now accept a list of symbols.
This means you can now easily filter several major modes, as well
as a single mode.

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** Gnus

+++
*** The nnimap backend now has support for IMAP namespaces.
This feature can be enabled by setting the new 'nnimap-use-namespaces'
server variable to non-nil.

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* Startup Changes in Emacs 27.1
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+++
** Emacs can now be configured using an early init file.
The file is called 'early-init.el', in 'user-emacs-directory'.  It is
loaded very early in the startup process: before graphical elements
such as the tool bar are initialized, and before the package manager
is initialized.  The primary purpose is to allow customizing how the
package system is initialized given that initialization now happens
before loading the regular init file (see below).

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We recommend against putting any customizations in this file that
don't need to be set up before initializing installed add-on packages,
because the early init file is read too early into the startup
process, and some important parts of the Emacs session, such as
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'window-system' and other GUI features, are not yet set up, which could
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make some customization fail to work.

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+++
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** Installed packages are now activated *before* loading the init file.
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This is part of a change intended to eliminate the behavior of
package.el inserting a call to 'package-initialize' into the init
file, which was previously done when Emacs was started.  As a result
of this change, it is no longer necessary to call 'package-initialize'
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in your init file.

However, if your init file changes the values of 'package-load-list' or
'package-user-dir', or sets 'package-enable-at-startup' to nil then it won't
work right without some adjustment:
- you can move that code to the early init file (see above), so those settings
  apply before Emacs tries to activate the packages.
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- you can use the new 'package-quickstart' so activation of packages does not
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  need to pay attention to 'package-load-list' or 'package-user-dir' any more.
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---
** Emacs now notifies systemd when startup finishes or shutdown begins.
Units that are ordered after 'emacs.service' will only be started
after Emacs has finished initialization and is ready for use.
(If your Emacs is installed in a non-standard location and you copied the
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emacs.service file to eg "~/.config/systemd/user/", you will need to copy
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the new version of the file again.)

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* Changes in Emacs 27.1
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** emacsclient

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+++
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*** emacsclient now supports the 'EMACS_SOCKET_NAME' environment variable.
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The behavior is identical to 'EMACS_SERVER_FILE', in that the
command-line value specified via '--socket-name' will override the
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environment, and the natural default to TMPDIR, then "/tmp", continues
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to apply.
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+++
*** Emacs and emacsclient now default to $XDG_RUNTIME_DIR/emacs
as the directory for client/server sockets, if Emacs is running
under an X Window System desktop that sets the XDG_RUNTIME_DIR
environment variable to indicate where session sockets should go.
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To get the old, less-secure behavior, you can set the
EMACS_SOCKET_NAME environment variable to an appropriate value.
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---
*** When run by root, emacsclient no longer connects to non-root sockets.
(Instead you can use Tramp methods to run root commands in a non-root Emacs.)

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** The function 'read-passwd' uses '*' as default character to hide passwords.

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---
** The new option 'tooltip-resize-echo-area' avoids truncating tooltip text
on GUI frames when tooltips are displayed in the echo area.  Instead,
it resizes the echo area as needed to accommodate the full tool-tip
text.

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---
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** Show mode line tooltips only if the corresponding action applies.
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Customize the option 'mode-line-default-help-echo' to restore the old
behavior where the tooltip text is also shown when the corresponding
action does not apply.

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+++
** New hook 'server-after-make-frame-hook'.
This hook is a convenient place to perform initializations in daemon
mode which require GUI features to be available.  One example is
restoration of the previous session using the desktop.el package: put
the call to 'desktop-read' in this hook, if you want the GUI settings
to be restored, or if desktop.el needs to interact with you during
restoration of the session.

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+++
** New function 'logcount' calculates an integer's Hamming weight.

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+++
** New function 'libxml-available-p'.
This function returns non-nil if libxml support is both compiled in
and available at run time.  Lisp programs should use this function to
detect built-in libxml support, instead of testing for that
indirectly, e.g., by checking that functions like
'libxml-parse-html-region' return nil.

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+++
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** 'libxml-parse-xml-region' and 'libxml-parse-html' region take
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a parameter that's called DISCARD-COMMENTS, but it really only
discards the top-level comment.  Therefore this parameter is now
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obsolete, and the new utility function 'xml-remove-comments' can be
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used to remove comments before calling the libxml functions to parse
the data.

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+++
** The Network Security Manager now allows more fine-grained control
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of what checks to run via the 'network-security-protocol-checks'
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variable.

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** TLS connections have their security tightened by default.
Most of the checks for outdated, believed-to-be-weak TLS algorithms
and ciphers are now switched on by default.  By default, the NSM will
flag connections using these weak algorithms and ask users whether to
allow them.  To get the old behavior back (where certificates are
checked for validity, but no warnings about weak cryptography are
issued), you can either set 'network-security-protocol-checks' to nil,
or adjust the elements in that variable to only happen on the 'high'
security level (assuming you use the 'medium' level).
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+++
** New function 'fill-polish-nobreak-p', to be used in 'fill-nobreak-predicate'.
It blocks line breaking after a one-letter word, also in the case when
this word is preceded by a non-space, but non-alphanumeric character.

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+++
** The limit on repetitions in regexps has been raised to 2^16-1.
It was previously limited to 2^15-1.  For example, the following
regular expression was previously invalid, but is now accepted:

   x\{32768\}

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---
** The German prefix and postfix input methods now support Capital sharp S.

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---
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** New input methods 'hawaiian-postfix' and 'hawaiian-prefix'.
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** New function 'exec-path'.
This function by default returns the value of the corresponding
variable, but can optionally return the equivalent of 'exec-path'
from a remote host.
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+++
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** The function 'executable-find' supports an optional argument REMOTE.
This triggers to search the program on the remote host as indicated by
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'default-directory'.

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+++
** New variable 'auto-save-no-message'.
When set to t, no message will be shown when auto-saving (default
value: nil).

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---
** The value of 'make-cursor-line-fully-visible' can now be a function.
In addition to nil or non-nil, the value can now be a predicate
function.  Follow mode uses this to control scrolling of its windows
when the last screen line in a window is not fully visible.

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+++
** New variable 'emacs-repository-branch'.
It reports the git branch from which Emacs was built.

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* Editing Changes in Emacs 27.1
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** New command 'make-empty-file'.

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---
** New variable 'x-wait-for-event-timeout'.
This controls how long Emacs will wait for updates to the graphical
state to take effect (making a frame visible, for example).

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+++
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** New user option 'electric-quote-replace-double'.
This option controls whether '"' is replaced in 'electric-quote-mode',
in addition to other quote characters.  If non-nil, ASCII double-quote
characters that quote text "like this" are replaced by double
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typographic quotes, “like this”, in text modes, and in comments in
non-text modes.
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---
** New user option 'flyspell-case-fold-duplications'.
This option controls whether Flyspell mode considers consecutive words
to be duplicates if they are not in the same case.  If non-nil, the
default, words are considered to be duplicates even if their letters'
case does not match.

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---
** 'write-abbrev-file' now includes special properties.
'write-abbrev-file' now writes special properties like ':case-fixed'
for abbrevs that have them.

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+++
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** 'write-abbrev-file' skips empty tables.
'write-abbrev-file' now skips inserting a 'define-abbrev-table' form for
tables which do not have any non-system abbrevs to save.
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** The new functions and commands 'text-property-search-forward' and
'text-property-search-backward' have been added.  These provide an
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interface that's more like functions like 'search-forward'.
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---
** More commands support noncontiguous rectangular regions, namely
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'upcase-dwim', 'downcase-dwim', 'replace-string', 'replace-regexp'.
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+++
** When asked to visit a large file, Emacs now offers visiting it literally.
Previously, Emacs would only ask for confirmation before visiting
large files.  Now it also offers a third alternative: to visit the
file literally, as in 'find-file-literally', which speeds up
navigation and editing of large files.

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---
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** 'add-dir-local-variable' now uses dotted pair notation syntax to
write alists of variables to ".dir-locals.el".  This is the same
syntax that you can see in the example of a ".dir-locals.el" file in
the node "(emacs) Directory Variables" of the user manual.
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* Changes in Specialized Modes and Packages in Emacs 27.1
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** map.el
*** Now defined via generic functions that can be extended via cl-defmethod.
*** Deprecate the 'map-put' macro in favor of a new 'map-put!' function.
*** map-contains-key now returns a boolean rather than the key.
*** Deprecate the 'testfn' args of 'map-elt' and 'map-contains-key'.

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---
** Follow mode
In the current follow group of windows, "ghost" cursors are no longer
displayed in the non-selected follow windows.  To get the old behavior
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back, customize 'follow-hide-ghost-cursors' to nil.
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** Windmove

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*** 'windmove-create-window' when non-nil makes a new window on moving off
the edge of the frame.

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*** Windmove supports directional window display and selection.
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The new command 'windmove-display-default-keybindings' binds default
keys with provided modifiers (by default, Shift-Meta) to the commands
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that display the next buffer in the window at the specified direction.
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This is like 'windmove-default-keybindings' that binds keys to commands
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that select the window in the specified direction, but additionally it
displays the buffer from the next command in that window.  For example,
'S-M-right C-h i' displays the *Info* buffer in the right window,
creating the window if necessary.  A special key can be customized to
display the buffer in the same window, for example, 'S-M-0 C-h e'
displays the *Messages* buffer in the same window.

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*** Windmove also supports directional window deletion.
The new command 'windmove-delete-default-keybindings' binds default
keys with provided prefix (by default, C-x) and modifiers (by default,
Shift) to the commands that delete the window in the specified
direction.  For example, 'C-x S-down' deletes the window below.
With a prefix arg 'C-u', deletes the selected window and selects
the window that was in the specified direction.
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** Octave mode
The mode is automatically enabled in files that start with the
'function' keyword.

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** project.el
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*** New commands 'project-search' and 'project-query-replace'.
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** Etags
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+++
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*** 'next-file' is now an obsolete alias of 'tags-next-file'.

*** 'tags-loop-revert-buffers' is an obsolete alias of
'multifile-revert-buffers'.

*** The 'tags-loop-continue' function along with the
'tags-loop-operate' and 'tags-loop-scan' variables are now obsolete;
use the new 'multifile-initialize' and 'multifile-continue' functions
instead.
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** bibtex
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---
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*** New commands 'bibtex-next-entry' and 'bibtex-previous-entry'.
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In 'bibtex-mode-map', 'forward-paragraph' and 'backward-paragraph' are
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remapped to these, respectively.

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** Dired

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*** New command 'dired-create-empty-file'.

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** Change Logs and VC

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*** Recording ChangeLog entries doesn't require an actual file.
If a ChangeLog file doesn't exist, and if the new variable
'add-log-dont-create-changelog-file' is non-nil (which is the
default), commands such as 'C-x 4 a' will add log entries to a
suitable named temporary buffer.  (An existing ChangeLog file will
still be used if it exists.)  Set the variable to nil to get the
previous behavior of always creating a buffer that visits a ChangeLog
file.
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*** New customizable variable 'vc-find-revision-no-save'.
With non-nil, 'vc-find-revision' doesn't write the created buffer to file.

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*** New customizable variable 'vc-git-grep-template'.
This new variable allows customizing the default arguments passed to
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'git-grep' when 'vc-git-grep' is used.
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*** Command 'vc-git-stash' now respects marks in the '*vc-dir*' buffer.
When some files are marked, only those are stashed.
When no files are marked, all modified files are stashed, as before.

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*** The new hook 'vc-retrieve-tag-hook' runs after retrieving a tag.

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---
*** 'vc-hg' now invokes 'smerge-mode' when visiting files.
Code that attempted to invoke 'smerge-mode' when visiting an Hg file
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with conflicts existed in earlier versions of Emacs, but incorrectly
never detected a conflict due to invalid assumptions about cached
values.

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+++
*** 'C-u C-x v D' ('vc-root-version-diff') prompts for two revisions
and compares their entire trees.

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** Diff mode
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*** Hunks are now automatically refined by default.
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To disable it, set the new defcustom 'diff-font-lock-refine' to nil.

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*** File headers can be shortened, mimicking Magit's diff format.
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To enable it, set the new defcustom 'diff-font-lock-prettify' to t.
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*** Prefix arg of 'diff-goto-source' means jump to the old revision
of the file under version control if point is on an old changed line,
or to the new revision of the file otherwise.

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** Browse-url
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*** The function 'browse-url-emacs' can now visit a URL in selected window.
It now treats the optional 2nd argument to mean that the URL should be
shown in the currently selected window.

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** Comint
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*** 'send-invisible' is now an obsolete alias for 'comint-send-invisible'.
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Also, 'shell-strip-ctrl-m' is declared obsolete.

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*** 'C-c .' ('comint-insert-previous-argument') no longer interprets '&'.
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This feature caused problems when '&&' was present in the previous
command.  Since this command emulates 'M-.' in Bash and zsh, neither
of which treats '&' specially, the feature was removed for
compatibility with these shells.

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*** 'comint-insert-previous-argument' can now count arguments from the end.
By default, invoking 'C-c .' with a numeric argument N would copy the
Nth argument, counting from the first one.  But if the new option
'comint-insert-previous-argument-from-end' is non-nil, it will copy
the Nth argument counting from the last one.  Thus 'C-c .' can now
better emulate 'M-.' in both Bash and zsh, since the former counts
from the beginning of the arguments, while the latter counts from the
end.
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** SQL

*** Installation of 'sql-indent' from ELPA is strongly encouraged.
This package support sophisticated rules for properly indenting SQL
statements.  SQL is not like other programming languages like C, Java,
or Python where code is sparse and rules for formatting are fairly
well established. Instead SQL is more like COBOL (from which it came)
and code tends to be very dense and line ending decisions driven by
syntax and line length considerations to make readable code.
Experienced SQL developers may prefer to rely upon existing Emacs
facilities for formatting code but the 'sql-indent' package provides
facilities to aid more casual SQL developers layout queries and
complex expressions.

*** 'sql-use-indent-support' (default t) enables SQL indention support.
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The 'sql-indent' package from ELPA must be installed to get the
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indentation support in 'sql-mode' and 'sql-interactive-mode'.

*** 'sql-mode-hook' and 'sql-interactive-mode-hook' changed.
Both hook variables have had 'sql-indent-enable' added to their
default values. If youhave existing customizations to these variables,
you should make sure that the new default entry is included.

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** Term

---
*** 'term-read-noecho' is now obsolete, use 'read-passwd' instead.

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** Flymake

+++
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*** The variable 'flymake-diagnostic-types-alist' is obsolete.
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You should instead set properties on known diagnostic symbols, like
':error' and ':warning', as demonstrated in the Flymake manual.

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*** New customizable variable 'flymake-start-on-save-buffer'.
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Control whether Flymake starts checking the buffer on save.

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*** Flymake and backend functions may exchange hints about buffer changes.
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This enables more efficient backends.  See the docstring of
'flymake-diagnostic-functions' or the Flymake manual for details.

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** Package
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*** New function 'package-get-version' lets packages query their own version.
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Example use in auctex.el: '(defconst auctex-version (package-get-version))'
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*** New 'package-quickstart' feature.
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When 'package-quickstart' is non-nil, package.el precomputes a big autoloads
file so that activation of packages can be done much faster, which can speed up
your startup significantly.
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It also causes variables like 'package-user-dir' and 'package-load-list' to be
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consulted when 'package-quickstart-refresh' is run rather than at startup so
you don't need to set them in your early init file.

*** New function 'package-activate-all'.

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** Info

---
*** Info can now follow 'file://' protocol URLs.
The 'file://' URLs in Info documents can now be followed by passing
them to the 'browse-url' function, like the other protocols: ftp,
http, and https.  This allows to have references to local HTML files,
for example.

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** Xref

+++
*** New command 'xref-find-definitions-at-mouse'.
This command finds definitions of the identifier at the place of a
mouse click event, and is intended to be bound to a mouse event.

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+++
*** Changing 'xref-marker-ring-length' works after 'xref.el' is loaded.
Previously, setting 'xref-marker-ring-length' would only take effect
if set before 'xref.el' was loaded.

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** Ecomplete
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*** The ecomplete sorting has changed to a decay-based algorithm.
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This can be controlled by the new 'ecomplete-sort-predicate' variable.
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*** The 'ecompleterc' file is now placed in ~/.emacs.d/ecompleterc by default.
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Of course it will still find it if you have it in ~/.ecompleterc

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** Gnus
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*** A prefix argument to 'gnus-summary-limit-to-score' will limit reverse.
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Limit to articles with score at below.

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*** The function 'gnus-score-find-favorite-words' has been renamed
from 'gnus-score-find-favourite-words'.

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---
*** Gmane has been removed as an nnir backend, since Gmane no longer
has a search engine.

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*** Splitting mail on common mailing list headers has been added.
See the concept index in the Gnus manual for the 'match-list' entry.
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*** nil is no longer an allowed value for 'mm-text-html-renderer'.
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*** A new Gnus summary mode command, 'S A'
('gnus-summary-attach-article') can be used to attach the current
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article(s) to a pre-existing Message buffer, or create a new Message
buffer with the article(s) attached.

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---
*** New option 'nnir-notmuch-filter-group-names-function'.
This option controls whether and how to use Gnus search groups as
'path:' search terms to 'notmuch'.

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** erc

---
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*** 'erc-button-google-url' has been renamed 'erc-button-search-url'
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and its value has been changed to Duck Duck Go.

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** EUDC

*** XEmacs support has been removed.

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** eww/shr

*** When opening external links in eww/shr (typically with the
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'C-u RET' keystroke on a link), the link will be flashed with the new
'shr-selected-link' face to give the user feedback that the command
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has been executed.

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+++
*** New option 'shr-discard-aria-hidden'.
If set, shr will not render tags with attribute 'aria-hidden="true"'.
This attribute is meant to tell screen readers to ignore a tag.

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** Htmlfontify
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*** The functions 'hfy-color', 'hfy-color-vals' and
'hfy-fallback-color-values' and the variables 'hfy-fallback-color-map'
and 'hfy-rgb-txt-color-map' have been renamed from names that used
'colour' instead of 'color'.

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** Enriched mode supports the 'charset' text property.
You can add or modify the 'charset' text properties of text using the
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'Edit->Text Properties->Special Properties' menu, or by invoking the
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'facemenu-set-charset' command.  Documents in Enriched mode will be
saved with the charset properties, and those properties will be
restored when the file is visited.

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** Smtpmail
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Authentication mechanisms can be added via external packages, by
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defining new 'cl-defmethod' of 'smtpmail-try-auth-method'.
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** Footnote mode
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*** Support Hebrew-style footnotes
*** Footnote text lines are now aligned.
Can be controlled via the new variable 'footnote-align-to-fn-text'.

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** CSS mode

---
*** A new command 'css-cycle-color-format' for cycling between color
formats (e.g. "black" => "#000000" => "rgb(0, 0, 0)") has been added,
bound to 'C-c C-f'.

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---
*** CSS mode, SCSS mode, and Less CSS mode now have support for Imenu.

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** SGML mode

---
*** 'sgml-quote' now handles double quotes and apostrophes
when escaping text and in addition all numeric entities when
unescaping text.

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** Python mode

---
*** Python mode supports three different font lock decoration levels.
The maximum level is used by default; customize
'font-lock-maximum-decoration' to tone down the decoration.

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** Dired

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*** The new user option 'dired-create-destination-dirs' controls whether
'dired-do-copy' and 'dired-rename-file' should create non-existent
directories in the destination.

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** Help

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---
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*** Output format of 'C-h l' ('view-lossage') has changed.
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For convenience, 'view-lossage' now displays the last keystrokes
and commands in the same format as the edit buffer of
'edit-last-kbd-macro'.  This makes it possible to copy the lines from
the buffer generated by 'view-lossage' to the "*Edit Macro*" buffer
created by 'edit-last-kbd-macro', and to save the macro by 'C-c C-c'.
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---
*** The list of help commands produced by 'C-h C-h' ('help-for-help')
can now be searched via 'C-s'.

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** Ibuffer

---
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*** New filter 'ibuffer-filter-by-process'; bound to '/E'.
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** Search and Replace

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*** Isearch supports a prefix argument for 'C-s' ('isearch-repeat-forward')
and 'C-r' ('isearch-repeat-backward').  With a prefix argument, these
commands repeat the search for the specified occurrence of the search string.
A negative argument repeats the search in the opposite direction.
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This makes possible also to use a prefix argument for 'M-s .'
('isearch-forward-symbol-at-point') to find the next Nth symbol.
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*** To go to the first/last occurrence of the current search string
is possible now with new commands 'isearch-beginning-of-buffer' and
'isearch-end-of-buffer' bound to 'M-s M-<' and 'M-s M->' in Isearch.
With a numeric argument, they go to the Nth absolute occurrence
counting from the beginning/end of the buffer.  This complements
'C-s'/'C-r' that searches for the next Nth relative occurrence
with a numeric argument.

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*** 'isearch-lazy-count' shows the current match number and total number
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of matches in the Isearch prompt.  Customizable variables
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'lazy-count-prefix-format' and 'lazy-count-suffix-format' define the
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format of the current and the total number of matches in the prompt's
prefix and suffix respectively.

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*** 'lazy-highlight-buffer' highlights matches in the full buffer.
It is useful in combination with 'lazy-highlight-cleanup' customized to nil
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to leave matches highlighted in the whole buffer after exiting isearch.
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Also when 'lazy-highlight-buffer' prepares highlighting in the buffer,
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navigation through the matches without flickering is more smooth.
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'lazy-highlight-buffer-max-at-a-time' controls the number of matches to
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highlight in one iteration while processing the full buffer.

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+++
*** New isearch bindings.
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'C-M-w' in isearch changed from 'isearch-del-char' to the new function
'isearch-yank-symbol-or-char'.  'isearch-del-char' is now bound to
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'C-M-d'.
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+++
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*** New variable 'isearch-yank-on-move' provides options 't' and 'shift'
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to extend the search string by yanking text that ends at the new
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position after moving point in the current buffer.  'shift' extends
the search string by motion commands while holding down the shift key.
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*** 'isearch-allow-scroll' provides new option 'unlimited' to allow
scrolling any distance off screen.

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---
*** Isearch now remembers the regexp-based search mode for words/symbols
and case-sensitivity together with search strings in the search ring.

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---
*** Isearch now has its own tool-bar and menu-bar menu.

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** Debugger

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*** The Lisp Debugger is now based on 'backtrace-mode'.
Backtrace mode adds fontification and commands for changing the
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appearance of backtrace frames.  See the node "(elisp) Backtraces" in
the Elisp manual for documentation of the new mode and its commands.
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** Edebug

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*** The runtime behavior of Edebug's instrumentation can be changed
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using the new variables 'edebug-behavior-alist',
'edebug-after-instrumentation-function' and
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'edebug-new-definition-function'.  Edebug's behavior can be changed
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globally or for individual definitions.

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*** Edebug's backtrace buffer now uses 'backtrace-mode'.
Backtrace mode adds fontification, links and commands for changing the
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appearance of backtrace frames.  See the node "(elisp) Backtraces" in
the Elisp manual for documentation of the new mode and its commands.
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The binding of 'd' in Edebug's keymap is now 'edebug-pop-to-backtrace'
which replaces 'edebug-backtrace'.  Consequently Edebug's backtrace
windows now behave like those of the Lisp Debugger and of ERT, in that
when they appear they will be the selected window.

The new 'backtrace-goto-source' command, bound to 's', works in
Edebug's backtraces on backtrace frames whose source code has
been instrumented by Edebug.

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** Enhanced xterm support

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*** New variable 'xterm-set-window-title' controls whether Emacs sets
the XTerm window title.  This feature is experimental and is disabled
by default.
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** grep

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+++
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*** rgrep, lgrep and zrgrep now hide part of the command line
that contains a list of ignored directories and files.
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Clicking on the button with ellipsis unhides it.
The abbreviation can be disabled by the new option
'grep-find-abbreviate'.  The new command
'grep-find-toggle-abbreviation' toggles it interactively.
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** ERT

+++
*** New variable 'ert-quiet' allows to make ERT output in batch mode
less verbose by removing non-essential information.

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+++
*** ERT's backtrace buffer now uses 'backtrace-mode'.
Backtrace mode adds fontification and commands for changing the
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appearance of backtrace frames.  See the node "(elisp) Backtraces" in
the Elisp manual for documentation of the new mode and its commands.
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** Gamegrid

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---
*** Gamegrid now determines its default glyph size based on display
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dimensions, instead of always using 16 pixels.  As a result, Tetris,
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Snake and Pong are more playable on HiDPI displays.

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** Filecache

---
*** Completing filenames in the minibuffer via 'C-TAB' now uses the
styles as configured by the variable 'completion-styles'.

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** New macros 'thunk-let' and 'thunk-let*'.
These macros are analogue to 'let' and 'let*', but create bindings that
are evaluated lazily.

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** next-error

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+++
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*** New customizable variable 'next-error-find-buffer-function'.
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The value should be a function that determines how to find the
next buffer to be used by 'next-error' and 'previous-error'.  The
default is to use the last buffer that navigated to the current
error.

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*** New command 'next-error-select-buffer'.
It can be used to set any buffer as the next one to be used by
'next-error' and 'previous-error'.
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** nxml-mode

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---
*** The default value of 'nxml-sexp-element-flag' is now t.
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This means that pressing 'C-M-SPACE' now selects the entire tree by
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default, and not just the opening element.

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** Eshell

---
*** Expansion of history event designators is disabled by default.
To restore the old behavior, use

    (add-hook 'eshell-expand-input-functions
              #'eshell-expand-history-references)

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---
*** The function 'eshell-uniquify-list' has been renamed from
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'eshell-uniqify-list'.

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*** The function 'eshell/kill' is now able to handle signal switches.
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Previously 'eshell/kill' would fail if provided a kill signal to send
to the process.  It now accepts signals specified either by name or by
its number.

---
*** Emacs now follows symlinks in history-related files.
The files specified by 'eshell-history-file-name' and
'eshell-last-dir-ring-file-name' can include symlinks; these are now
followed when Emacs writes the relevant history variables to the disk.
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** Shell

---
*** Program name completion inside remote shells works now as expected.

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** Pcomplete
*** The function 'pcomplete-uniquify-list' has been renamed from
'pcomplete-uniqify-list'.

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** Auth-source

---
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*** The Secret Service backend supports the ':create' key now.
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** Tramp

+++
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*** New connection method "nextcloud", which allows to access OwnCloud
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or NextCloud hosted files and directories.

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+++
*** New connection method "rclone", which allows to access system
storages via the 'rclone' program.  This feature is experimental.

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+++
*** New connection method "sudoedit", which allows to edit local files
with different user credentials.  Contrary to the "sudo" method, no
session is run permanently in the background.  This is for security
reasons.

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+++
*** Connection methods "obex" and "synce" are removed, because they
are obsoleted in GVFS.

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+++
*** Validated passwords are saved by auth-source backends which support this.

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*** During user and host name completion in the minibuffer, results
from auth-source search are taken into account.  This can be disabled
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by setting the user option 'tramp-completion-use-auth-sources' to nil.
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+++
*** The user option 'tramp-ignored-file-name-regexp' allows to disable
Tramp for some look-alike remote file names.

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+++
*** For some connection methods, like "su" or "sudo", the host name in
ad-hoc multi-hop file names must match the previous hop.

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*** For the connection methods "sudo" and "doas" there exists a
timeout, after which the underlying session is disabled.  This is for
security reasons.

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** Rcirc

---
*** New user option 'rcirc-url-max-length'.
Setting this option to an integer causes URLs displayed in Rcirc
buffers to be truncated to that many characters.

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** Register
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---
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*** The return value of method 'register-val-describe' includes the
names of buffers shown by the windows of a window configuration.

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---
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** The options.el library has been removed.
It was obsolete since Emacs 22.1, replaced by customize.

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** The tls.el and starttls.el libraries are now marked obsolete.
Use of built-in libgnutls based functionality (described in the Emacs
GnuTLS manual) is recommended instead.

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** Message

+++
*** Messages can now be systematically encrypted
when the PGP keyring contains a public key for every recipient.  To
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achieve this, add 'message-sign-encrypt-if-all-keys-available' to
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'message-send-hook'.

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---
*** When replying a message that have addresses on the form
'"foo@bar.com" <foo@bar.com>', Message will elide the repeated "name"
from the address field in the response.

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---
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*** The default of 'message-forward-as-mime' has changed from t to nil
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as it has been reported that many recipients can't read forwards that
are formatted as MIME digests.

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+++
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*** 'message-forward-included-headers' has changed its default to
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exclude most headers when forwarding.

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** EasyPG

---
*** 'epa-pinentry-mode' is renamed to 'epg-pinentry-mode'.
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It now applies to epg functions as well as epa functions.

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---
*** The alias functions 'epa--encode-coding-string',
'epa--decode-coding-string', and 'epa--select-safe-coding-system' have
been removed.  Use 'encode-coding-string', 'decode-coding-string', and
'select-safe-coding-system' instead.

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** Rmail

+++
*** New user option 'rmail-output-reset-deleted-flag'.
If this option is non-nil, messages appended to an output file by the
'rmail-output' command have their Deleted flag reset.

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*** The command 'rmail-summary-by-senders' with an empty argument
selects the messages to summarize with a regexp that matches the
sender of the current message.

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** Threads

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*** New variable 'main-thread' holds Emacs's main thread.
This is handy in Lisp programs that run on a non-main thread and want
to signal the main thread, e.g., when they encounter an error.

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*** 'thread-join' returns the result of the finished thread now.

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*** 'thread-signal' does not propagate errors to the main thread.
Instead, error messages are just printed in the main thread.

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---
*** 'thread-alive-p' is now obsolete, use 'thread-live-p' instead.

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*** New command 'list-threads' shows Lisp threads.
See the current list of live threads in a tabulated-list buffer which
automatically updates.  In the buffer, you can use 's q' or 's e' to
signal a thread with quit or error respectively, or get a snapshot
backtrace with 'b'.
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** thingatpt.el supports a new "thing" called 'uuid'.
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A symbol 'uuid' can be passed to 'thing-at-point' and it returns the
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UUID at point.

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** Interactive automatic highlighting
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*** 'highlight-regexp' can now highlight subexpressions.
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The new command accepts a prefix numeric argument to choose the
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subexpression.
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** Mouse display of minor mode menu

---
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*** 'minor-mode-menu-from-indicator' now displays full minor mode name.
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When there is no menu for a mode, display the mode name after the
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indicator instead of just the indicator (which is sometimes cryptic).
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* New Modes and Packages in Emacs 27.1
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** multifile.el lets one setup multifile operations like search&replace.
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** Emacs can now visit files in archives as if they were directories.
This feature uses Tramp and works only on systems which support GVFS,
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i.e. GNU/Linux, roughly spoken.  See the node "(tramp) Archive file
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names" in the Tramp manual for full documentation of these facilities.

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** New library for writing JSONRPC applications (https://jsonrpc.org).
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The 'jsonrpc' library enables writing Emacs Lisp applications that
rely on this protocol.  Since the protocol is designed to be
transport-agnostic, the library provides an API to implement new
transport strategies as well as a separate API to use them.  A
transport implementation for process-based communication, such as is
used by the Language Server Protocol (LSP), is readily available.

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+++
** Backtrace mode improves viewing of Elisp backtraces.
Backtrace mode adds pretty printing, fontification and ellipsis
expansion to backtrace buffers produced by the Lisp debugger, Edebug
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and ERT.  See the node "(elisp) Backtraces" in the Elisp manual for
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documentation of the new mode and its commands.

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* Incompatible Lisp Changes in Emacs 27.1

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** 'define-fringe-bitmap' is always defined, even when Emacs is built
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without any GUI support.

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---
** Just loading a theme's file no longer activates the theme's settings.
Loading a theme with 'M-x load-theme' still activates the theme, as it
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did before.  However, loading the theme's file with 'M-x load-file',
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or using 'require' or 'load' in a Lisp program, doesn't actually apply
the theme's settings until you either invoke 'M-x enable-theme' or
type 'M-x load-theme'.  (In a Lisp program, calling 'enable-theme' or
invoking 'load-theme' with NO-ENABLE argument omitted or nil has the
same effect of activating a theme whose file has been loaded.)  The
special case of the 'user' theme is an exception: it is frequently
used for ad-hoc customizations, so the settings of that theme are by
default applied immediately.

The variable 'custom--inhibit-theme-enable' controls this behavior;
its default value changed in Emacs 27.1.
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** The REPETITIONS argument of 'benchmark-run' can now also be a variable.
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** Interpretation of relative HOME directory has changed.
If $HOME is set to a relative file name, 'expand-file-name' now
interprets it relative to the directory where Emacs was started, not
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