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Clarify documentation of before/after-change-functions

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* doc/lispref/text.texi (Change Hooks): Clarify that the hooks are
not called in balanced pairs.
This commit is contained in:
Eli Zaretskii 2016-08-09 19:52:50 +03:00
parent 3c9cb57c6f
commit f785ff45d5
1 changed files with 15 additions and 8 deletions
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doc/lispref/text.texi
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@ -4676,10 +4676,10 @@ group you start for any given buffer should be the last one finished.
@cindex change hooks @cindex change hooks
@cindex hooks for text changes @cindex hooks for text changes
These hook variables let you arrange to take notice of all changes in These hook variables let you arrange to take notice of changes in
all buffers (or in a particular buffer, if you make them buffer-local). buffers (or in a particular buffer, if you make them buffer-local).
See also @ref{Special Properties}, for how to detect changes to specific See also @ref{Special Properties}, for how to detect changes to
parts of the text. specific parts of the text.
The functions you use in these hooks should save and restore the match The functions you use in these hooks should save and restore the match
data if they do anything that uses regular expressions; otherwise, they data if they do anything that uses regular expressions; otherwise, they
@ -4687,8 +4687,8 @@ will interfere in bizarre ways with the editing operations that call
them. them.
@defvar before-change-functions @defvar before-change-functions
This variable holds a list of functions to call before any buffer This variable holds a list of functions to call before most buffer
modification. Each function gets two arguments, the beginning and end modifications. Each function gets two arguments, the beginning and end
of the region that is about to change, represented as integers. The of the region that is about to change, represented as integers. The
buffer that is about to change is always the current buffer. buffer that is about to change is always the current buffer.
@end defvar @end defvar
@ -4706,8 +4706,15 @@ for the changed text, its length is simply the difference between the
first two arguments. first two arguments.
@end defvar @end defvar
Output of messages into the @file{*Messages*} buffer does not Output of messages into the @file{*Messages*} buffer does not call
call these functions. these functions, and neither do certain internal buffer changes, such
as changes in buffers created by Emacs internally for certain jobs,
that should not be visible to Lisp programs.
Do @emph{not} expect the before-change hooks and the after-change
hooks be called in balanced pairs around each buffer change. These
hooks are provided on the assumption that Lisp programs will use
either before- or the after-change hooks, but not both.
@defmac combine-after-change-calls body@dots{} @defmac combine-after-change-calls body@dots{}
The macro executes @var{body} normally, but arranges to call the The macro executes @var{body} normally, but arranges to call the