@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1999, 2002-2016 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.

@c This node must have no pointers.

@node Antinews
@appendix Emacs 23 Antinews
@c Update the elisp.texi Antinews menu entry with the above version number.

For those users who live backwards in time, here is information about
downgrading to Emacs version 23.4.  We hope you will enjoy the greater
simplicity that results from the absence of many Emacs @value{EMACSVER}
features.

@section Old Lisp Features in Emacs 23

@itemize @bullet
@item
Support for lexical scoping has been removed; all variables are
dynamically scoped.  The @code{lexical-binding} variable has been
removed, and so has the @var{lexical} argument to @code{eval}.  The
@code{defvar} and @code{defconst} forms no longer mark variables as
dynamic, since all variables are dynamic.

Having only dynamic binding follows the spirit of Emacs extensibility,
for it allows any Emacs code to access any defined variable with a
minimum of fuss.  But @xref{Dynamic Binding Tips}, for tips to avoid
making your programs hard to understand.

@item
Calling a minor mode function from Lisp with a @code{nil} or omitted argument
does not enable the minor mode unconditionally; instead, it toggles
the minor mode---which is the straightforward thing to do, since that
is the behavior when invoked interactively.  One downside is that it
is more troublesome to enable minor modes from hooks; you have to do
something like

@example
(add-hook 'foo-hook (lambda () (bar-mode 1)))
@end example

@noindent
or define @code{turn-on-bar-mode} and call that from the hook.

@item
The @code{prog-mode} dummy major mode has been removed.  Instead of
using it as a crutch to meet programming mode conventions, you should
explicitly ensure that your mode follows those conventions.
@xref{Major Mode Conventions}.

@item
Emacs no longer supports bidirectional display and editing.  Since
there is no need to worry about the insertion of right-to-left text
messing up how lines and paragraphs are displayed, the function
@code{bidi-string-mark-left-to-right} has been removed; so have many
other functions and variables related to bidirectional display.
Unicode directionality characters like @code{U+200E} LEFT-TO-RIGHT
MARK have no special effect on display.

@item
Emacs windows now have most of their internal state hidden from Lisp.
Internal windows are no longer visible to Lisp; functions such as
@code{window-parent}, window parameters related to window arrangement,
and window-local buffer lists have all been removed.  Functions for
resizing windows can delete windows if they become too small.

The action-function feature for controlling buffer display has
been removed, including @code{display-buffer-overriding-action} and
related variables, as well as the @var{action} argument to
@code{display-buffer} and other functions.  The way to
programmatically control how Emacs chooses a window to display a
buffer is to bind the right combination of @code{pop-up-frames} and
other variables.

@item
The standard completion interface has been simplified, eliminating the
@code{completion-extra-properties} variable, the @code{metadata}
action flag for completion functions, and the concept of
completion categories.  Lisp programmers may now find the choice
of methods for tuning completion less bewildering, but if a package
finds the streamlined interface insufficient for its needs, it must
implement its own specialized completion feature.

@item
@code{copy-directory} now behaves the same whether or not the
destination is an existing directory: if the destination exists, the
@emph{contents} of the first directory are copied into it (with
subdirectories handled recursively), rather than copying the first
directory into a subdirectory.

@item
The @var{trash} arguments for @code{delete-file} and
@code{delete-directory} have been removed.  The variable
@code{delete-by-moving-to-trash} must now be used with care; whenever
it is non-@code{nil}, all calls to @code{delete-file} or
@code{delete-directory} use the trash.

@item
Because Emacs no longer supports SELinux file contexts, the
@var{preserve-selinux-context} argument to @code{copy-file} has been
removed.  The return value of @code{backup-buffer} no longer has an
entry for the SELinux file context.

@item
For mouse click input events in the text area, the Y pixel coordinate
in the @var{position} list (@pxref{Click Events}) now counts from the
top of the header line, if there is one, rather than the top of the
text area.

@item
Bindings in menu keymaps (@pxref{Format of Keymaps}) now sometimes get
an additional @var{cache} entry in their definitions, like this:

@example
(@var{type} @var{item-name} @var{cache} . @var{binding})
@end example

@noindent
The @var{cache} entry is used internally by Emacs to record equivalent
keyboard key sequences for invoking the same command; Lisp programs
should never use it.
@c Not really NEWS-worthy then...

@item
The @code{gnutls} library has been removed, and the function
@code{open-network-stream} correspondingly simplified.
Lisp programs that want an encrypted network connection must now call
external utilities such as @command{starttls} or @command{gnutls-cli}.

@item
Tool bars can no longer display separators, which frees up several
pixels of space on each graphical frame.

@item
As part of the ongoing quest for simplicity, many other functions and
variables have been eliminated.
@end itemize
