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Document 'major-mode-suspend' and 'major-mode-restore'

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* doc/lispref/modes.texi (Major Modes): Document
'major-mode-suspend' and 'major-mode-restore'.  (Bug#31551)

* etc/NEWS: Mark the corresponding entry as documented in
manuals.
This commit is contained in:
Eli Zaretskii 2018-06-22 11:48:38 +03:00
parent a5511956b4
commit 4e15d26313
2 changed files with 25 additions and 4 deletions
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22
doc/lispref/modes.texi
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@ -197,6 +197,7 @@ from the buffer-local hook list instead of from the global hook list.
@cindex major mode
@cindex major mode command
@cindex suspend major mode temporarily
Major modes specialize Emacs for editing or interacting with
particular kinds of text. Each buffer has exactly one major mode at a
time. Every major mode is associated with a @dfn{major mode command},
@ -205,7 +206,8 @@ switching to that mode in the current buffer, by setting various
buffer-local variables such as a local keymap. @xref{Major Mode
Conventions}. Note that unlike minor modes there is no way to ``turn
off'' a major mode, instead the buffer must be switched to a different
one.
one. However, you can temporarily @dfn{suspend} a major mode and later
@dfn{restore} the suspended mode, see below.
The least specialized major mode is called @dfn{Fundamental mode},
which has no mode-specific definitions or variable settings.
@ -216,6 +218,24 @@ commands, it does @emph{not} run any mode hooks (@pxref{Major Mode
Conventions}), since you are not supposed to customize this mode.
@end deffn
@defun major-mode-suspend
This function works like @code{fundamental-mode}, in that it kills all
buffer-local variables, but it also records the major mode in effect,
so that it could subsequently be restored. This function and
@code{major-mode-restore} (described next) are useful when you need to
put a buffer under some specialized mode other than the one Emacs
chooses for it automatically (@pxref{Auto Major Mode}), but would also
like to be able to switch back to the original mode later.
@end defun
@defun major-mode-restore &optional avoided-modes
This function restores the major mode recorded by
@code{major-mode-suspend}. If no major mode was recorded, this
function calls @code{normal-mode} (@pxref{Auto Major Mode,
normal-mode}), but tries to force it not to choose any modes in
@var{avoided-modes}, if that argument is non-@code{nil}.
@end defun
The easiest way to write a major mode is to use the macro
@code{define-derived-mode}, which sets up the new mode as a variant of
an existing major mode. @xref{Derived Modes}. We recommend using

7
etc/NEWS
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@ -658,9 +658,10 @@ manual for more details.
* Lisp Changes in Emacs 27.1
** New functions 'major-mode-suspend' and 'major-mode-restore'
Used when switching temporarily to another major mode, e.g. for hexl-mode,
or to switch between c-mode and image-mode in XPM.
+++
** New functions 'major-mode-suspend' and 'major-mode-restore'.
Use them when switching temporarily to another major mode, e.g. for
'hexl-mode', or to switch between 'c-mode' and 'image-mode' in XPM.
+++
** New macro 'dolist-with-progress-reporter'.