@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2004
@c Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/searching
Here is a complicated regexp which was formerly used by Emacs to
recognize the end of a sentence together with any whitespace that
-follows. It was used as the variable @code{sentence-end}. (Its value
-nowadays contains alternatives for @samp{.}, @samp{?} and @samp{!} in
-other character sets.)
+follows. (Nowadays Emacs uses a similar but more complex default
+regexp constructed by the function @code{sentence-end}.
+@xref{Standard Regexps}.)
First, we show the regexp as a string in Lisp syntax to distinguish
spaces from tab characters. The string constant begins and ends with a
The first part of the pattern is a character alternative that matches
any one of three characters: period, question mark, and exclamation
mark. The match must begin with one of these three characters. (This
-is the one point where the new value of @code{sentence-end} differs
-from the old. The new value also lists sentence ending
-non-@acronym{ASCII} characters.)
+is one point where the new default regexp used by Emacs differs from
+the old. The new value also allows some non-@acronym{ASCII}
+characters that end a sentence without any following whitespace.)
@item []\"')@}]*
The second part of the pattern matches any closing braces and quotation
@end example
@end defun
+@defun looking-back regexp &optional limit
+This function returns @code{t} if @var{regexp} matches text before
+point, ending at point, and @code{nil} otherwise.
+
+Because regular expression matching works only going forward, this is
+implemented by searching backwards from point for a match that ends at
+point. That can be quite slow if it has to search a long distance.
+You can bound the time required by specifying @var{limit}, which says
+not to search before @var{limit}. In this case, the match that is
+found must begin at or after @var{limit}.
+
+@example
+@group
+---------- Buffer: foo ----------
+I read "@point{}The cat in the hat
+comes back" twice.
+---------- Buffer: foo ----------
+
+(looking-back "read \"" 3)
+ @result{} t
+(looking-back "read \"" 4)
+ @result{} nil
+@end group
+@end example
+@end defun
+
@node POSIX Regexps
@section POSIX Regular Expression Searching
@end defvar
@defvar sentence-end
-This is the regular expression describing the end of a sentence. (All
-paragraph boundaries also end sentences, regardless.) The (slightly
-simplified) default value is:
-
-@example
-"[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*"
-@end example
-
-This means a period, question mark or exclamation mark (the actual
-default value also lists their alternatives in other character sets),
-followed optionally by closing parenthetical characters, followed by
-tabs, spaces or new lines.
-
-For a detailed explanation of this regular expression, see @ref{Regexp
-Example}.
+If non-@code{nil}, the value should be a regular expression describing
+the end of a sentence, including the whitespace following the
+sentence. (All paragraph boundaries also end sentences, regardless.)
+
+If the value is @code{nil}, the default, then the function
+@code{sentence-end} has to construct the regexp. That is why you
+should always call the function @code{sentence-end} to obtain the
+regexp to be used to recognize the end of a sentence.
@end defvar
+@defun sentence-end
+This function returns the value of the variable @code{sentence-end},
+if non-@code{nil}. Otherwise it returns a default value based on the
+values of the variables @code{sentence-end-double-space}
+(@pxref{Definition of sentence-end-double-space}),
+@code{sentence-end-without-period} and
+@code{sentence-end-without-space}.
+@end defun
+
@ignore
arch-tag: c2573ca2-18aa-4839-93b8-924043ef831f
@end ignore