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+@c -*-texinfo-*-
+@c This is part of the XEmacs Lisp Reference Manual.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
+@c See the file lispref.texi for copying conditions.
+@setfilename ../../info/searching.info
+@node Searching and Matching, Syntax Tables, Text, Top
+@chapter Searching and Matching
+@cindex searching
+XEmacs provides two ways to search through a buffer for specified
+text: exact string searches and regular expression searches.  After a
+regular expression search, you can examine the @dfn{match data} to
+determine which text matched the whole regular expression or various
+portions of it.
+@menu
+* String Search::         Search for an exact match.
+* Regular Expressions::   Describing classes of strings.
+* Regexp Search::         Searching for a match for a regexp.
+* POSIX Regexps::         Searching POSIX-style for the longest match.
+* Search and Replace::	  Internals of @code{query-replace}.
+* Match Data::            Finding out which part of the text matched
+various parts of a regexp, after regexp search.
+* Searching and Case::    Case-independent or case-significant searching.
+* Standard Regexps::      Useful regexps for finding sentences, pages,...
+@end menu
+The @samp{skip-chars@dots{}} functions also perform a kind of searching.
+@xref{Skipping Characters}.
+@node String Search
+@section Searching for Strings
+@cindex string search
+These are the primitive functions for searching through the text in a
+buffer.  They are meant for use in programs, but you may call them
+interactively.  If you do so, they prompt for the search string;
+@var{limit} and @var{noerror} are set to @code{nil}, and @var{repeat}
+is set to 1.
+@deffn Command search-forward string &optional limit noerror repeat
+This function searches forward from point for an exact match for
+@var{string}.  If successful, it sets point to the end of the occurrence
+found, and returns the new value of point.  If no match is found, the
+value and side effects depend on @var{noerror} (see below).
+@c Emacs 19 feature
+In the following example, point is initially at the beginning of the
+line.  Then @code{(search-forward "fox")} moves point after the last
+letter of @samp{fox}:
+@example
+@group
+---------- Buffer: foo ----------
+@point{}The quick brown fox jumped over the lazy dog.
+---------- Buffer: foo ----------
+@end group
+@group
+(search-forward "fox")
+@result{} 20
+---------- Buffer: foo ----------
+The quick brown fox@point{} jumped over the lazy dog.
+---------- Buffer: foo ----------
+@end group
+@end example
+The argument @var{limit} specifies the upper bound to the search.  (It
+must be a position in the current buffer.)  No match extending after
+that position is accepted.  If @var{limit} is omitted or @code{nil}, it
+defaults to the end of the accessible portion of the buffer.
+@kindex search-failed
+What happens when the search fails depends on the value of
+@var{noerror}.  If @var{noerror} is @code{nil}, a @code{search-failed}
+error is signaled.  If @var{noerror} is @code{t}, @code{search-forward}
+returns @code{nil} and does nothing.  If @var{noerror} is neither
+@code{nil} nor @code{t}, then @code{search-forward} moves point to the
+upper bound and returns @code{nil}.  (It would be more consistent now
+to return the new position of point in that case, but some programs
+may depend on a value of @code{nil}.)
+If @var{repeat} is supplied (it must be a positive number), then the
+search is repeated that many times (each time starting at the end of the
+previous time's match).  If these successive searches succeed, the
+function succeeds, moving point and returning its new value.  Otherwise
+the search fails.
+@end deffn
+@deffn Command search-backward string &optional limit noerror repeat
+This function searches backward from point for @var{string}.  It is
+just like @code{search-forward} except that it searches backwards and
+leaves point at the beginning of the match.
+@end deffn
+@deffn Command word-search-forward string &optional limit noerror repeat
+@cindex word search
+This function searches forward from point for a ``word'' match for
+@var{string}.  If it finds a match, it sets point to the end of the
+match found, and returns the new value of point.
+@c Emacs 19 feature
+Word matching regards @var{string} as a sequence of words, disregarding
+punctuation that separates them.  It searches the buffer for the same
+sequence of words.  Each word must be distinct in the buffer (searching
+for the word @samp{ball} does not match the word @samp{balls}), but the
+details of punctuation and spacing are ignored (searching for @samp{ball
+boy} does match @samp{ball.  Boy!}).
+In this example, point is initially at the beginning of the buffer; the
+search leaves it between the @samp{y} and the @samp{!}.
+@example
+@group
+---------- Buffer: foo ----------
+@point{}He said "Please!  Find
+the ball boy!"
+---------- Buffer: foo ----------
+@end group
+@group
+(word-search-forward "Please find the ball, boy.")
+@result{} 35
+---------- Buffer: foo ----------
+He said "Please!  Find
+the ball boy@point{}!"
+---------- Buffer: foo ----------
+@end group
+@end example
+If @var{limit} is non-@code{nil} (it must be a position in the current
+buffer), then it is the upper bound to the search.  The match found must
+not extend after that position.
+If @var{noerror} is @code{nil}, then @code{word-search-forward} signals
+an error if the search fails.  If @var{noerror} is @code{t}, then it
+returns @code{nil} instead of signaling an error.  If @var{noerror} is
+neither @code{nil} nor @code{t}, it moves point to @var{limit} (or the
+end of the buffer) and returns @code{nil}.
+If @var{repeat} is non-@code{nil}, then the search is repeated that many
+times.  Point is positioned at the end of the last match.
+@end deffn
+@deffn Command word-search-backward string &optional limit noerror repeat
+This function searches backward from point for a word match to
+@var{string}.  This function is just like @code{word-search-forward}
+except that it searches backward and normally leaves point at the
+beginning of the match.
+@end deffn
+@node Regular Expressions
+@section Regular Expressions
+@cindex regular expression
+@cindex regexp
+A @dfn{regular expression} (@dfn{regexp}, for short) is a pattern that
+denotes a (possibly infinite) set of strings.  Searching for matches for
+a regexp is a very powerful operation.  This section explains how to write
+regexps; the following section says how to search for them.
+To gain a thorough understanding of regular expressions and how to use
+them to best advantage, we recommend that you study @cite{Mastering
+Regular Expressions, by Jeffrey E.F. Friedl, O'Reilly and Associates,
+1997}. (It's known as the "Hip Owls" book, because of the picture on its
+cover.)  You might also read the manuals to @ref{(gawk)Top},
+@ref{(ed)Top}, @cite{sed}, @cite{grep}, @ref{(perl)Top},
+@ref{(regex)Top}, @ref{(rx)Top}, @cite{pcre}, and @ref{(flex)Top}, which
+also make good use of regular expressions.
+The XEmacs regular expression syntax most closely resembles that of
+@cite{ed}, or @cite{grep}, the GNU versions of which all utilize the GNU
+@cite{regex} library.  XEmacs' version of @cite{regex} has recently been
+extended with some Perl--like capabilities, described in the next
+section.
+@menu
+* Syntax of Regexps::       Rules for writing regular expressions.
+* Regexp Example::          Illustrates regular expression syntax.
+@end menu
+@node Syntax of Regexps
+@subsection Syntax of Regular Expressions
+Regular expressions have a syntax in which a few characters are
+special constructs and the rest are @dfn{ordinary}.  An ordinary
+character is a simple regular expression that matches that character and
+nothing else.  The special characters are @samp{.}, @samp{*}, @samp{+},
+@samp{?}, @samp{[}, @samp{]}, @samp{^}, @samp{$}, and @samp{\}; no new
+special characters will be defined in the future.  Any other character
+appearing in a regular expression is ordinary, unless a @samp{\}
+precedes it.
+For example, @samp{f} is not a special character, so it is ordinary, and
+therefore @samp{f} is a regular expression that matches the string
+@samp{f} and no other string.  (It does @emph{not} match the string
+@samp{ff}.)  Likewise, @samp{o} is a regular expression that matches
+only @samp{o}.@refill
+Any two regular expressions @var{a} and @var{b} can be concatenated.  The
+result is a regular expression that matches a string if @var{a} matches
+some amount of the beginning of that string and @var{b} matches the rest of
+the string.@refill
+As a simple example, we can concatenate the regular expressions @samp{f}
+and @samp{o} to get the regular expression @samp{fo}, which matches only
+the string @samp{fo}.  Still trivial.  To do something more powerful, you
+need to use one of the special characters.  Here is a list of them:
+@need 1200
+@table @kbd
+@item .@: @r{(Period)}
+@cindex @samp{.} in regexp
+is a special character that matches any single character except a newline.
+Using concatenation, we can make regular expressions like @samp{a.b}, which
+matches any three-character string that begins with @samp{a} and ends with
+@samp{b}.@refill
+@item *
+@cindex @samp{*} in regexp
+is not a construct by itself; it is a quantifying suffix operator that
+means to repeat the preceding regular expression as many times as
+possible.  In @samp{fo*}, the @samp{*} applies to the @samp{o}, so
+@samp{fo*} matches one @samp{f} followed by any number of @samp{o}s.
+The case of zero @samp{o}s is allowed: @samp{fo*} does match
+@samp{f}.@refill
+@samp{*} always applies to the @emph{smallest} possible preceding
+expression.  Thus, @samp{fo*} has a repeating @samp{o}, not a
+repeating @samp{fo}.@refill
+The matcher processes a @samp{*} construct by matching, immediately, as
+many repetitions as can be found; it is "greedy".  Then it continues
+with the rest of the pattern.  If that fails, backtracking occurs,
+discarding some of the matches of the @samp{*}-modified construct in
+case that makes it possible to match the rest of the pattern.  For
+example, in matching @samp{ca*ar} against the string @samp{caaar}, the
+@samp{a*} first tries to match all three @samp{a}s; but the rest of the
+pattern is @samp{ar} and there is only @samp{r} left to match, so this
+try fails.  The next alternative is for @samp{a*} to match only two
+@samp{a}s.  With this choice, the rest of the regexp matches
+successfully.@refill
+Nested repetition operators can be extremely slow if they specify
+backtracking loops.  For example, it could take hours for the regular
+expression @samp{\(x+y*\)*a} to match the sequence
+@samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}.  The slowness is because
+Emacs must try each imaginable way of grouping the 35 @samp{x}'s before
+concluding that none of them can work.  To make sure your regular
+expressions run fast, check nested repetitions carefully.
+@item +
+@cindex @samp{+} in regexp
+is a quantifying suffix operator similar to @samp{*} except that the
+preceding expression must match at least once.  It is also "greedy".
+So, for example, @samp{ca+r} matches the strings @samp{car} and
+@samp{caaaar} but not the string @samp{cr}, whereas @samp{ca*r} matches
+all three strings.
+@item ?
+@cindex @samp{?} in regexp
+is a quantifying suffix operator similar to @samp{*}, except that the
+preceding expression can match either once or not at all.  For example,
+@samp{ca?r} matches @samp{car} or @samp{cr}, but does not match anything
+else.
+@item *?
+@cindex @samp{*?} in regexp
+works just like @samp{*}, except that rather than matching the longest
+match, it matches the shortest match.  @samp{*?} is known as a
+@dfn{non-greedy} quantifier, a regexp construct borrowed from Perl.
+@c Did perl get this from somewhere?  What's the real history of *? ?
+This construct very useful for when you want to match the text inside a
+pair of delimiters.  For instance, @samp{/\*.*?\*/} will match C
+comments in a string.  This could not be achieved without the use of
+greedy quantifier.
+This construct has not been available prior to XEmacs 20.4.  It is not
+available in FSF Emacs.
+@item +?
+@cindex @samp{+?} in regexp
+is the @samp{+} analog to @samp{*?}.
+@item \@{n,m\@}
+@c Note the spacing after the close brace is deliberate.
+@cindex @samp{\@{n,m\@} }in regexp
+serves as an interval quantifier, analogous to @samp{*} or @samp{+}, but
+specifies that the expression must match at least @var{n} times, but no
+more than @var{m} times.  This syntax is supported by most Unix regexp
+utilities, and has been introduced to XEmacs for the version 20.3.
+@item [ @dots{} ]
+@cindex character set (in regexp)
+@cindex @samp{[} in regexp
+@cindex @samp{]} in regexp
+@samp{[} begins a @dfn{character set}, which is terminated by a
+@samp{]}.  In the simplest case, the characters between the two brackets
+form the set.  Thus, @samp{[ad]} matches either one @samp{a} or one
+@samp{d}, and @samp{[ad]*} matches any string composed of just @samp{a}s
+and @samp{d}s (including the empty string), from which it follows that
+@samp{c[ad]*r} matches @samp{cr}, @samp{car}, @samp{cdr},
+@samp{caddaar}, etc.@refill
+The usual regular expression special characters are not special inside a
+character set.  A completely different set of special characters exists
+inside character sets: @samp{]}, @samp{-} and @samp{^}.@refill
+@samp{-} is used for ranges of characters.  To write a range, write two
+characters with a @samp{-} between them.  Thus, @samp{[a-z]} matches any
+lower case letter.  Ranges may be intermixed freely with individual
+characters, as in @samp{[a-z$%.]}, which matches any lower case letter
+or @samp{$}, @samp{%}, or a period.@refill
+To include a @samp{]} in a character set, make it the first character.
+For example, @samp{[]a]} matches @samp{]} or @samp{a}.  To include a
+@samp{-}, write @samp{-} as the first character in the set, or put it
+immediately after a range.  (You can replace one individual character
+@var{c} with the range @samp{@var{c}-@var{c}} to make a place to put the
+@samp{-}.)  There is no way to write a set containing just @samp{-} and
+@samp{]}.
+To include @samp{^} in a set, put it anywhere but at the beginning of
+the set.
+@item [^ @dots{} ]
+@cindex @samp{^} in regexp
+@samp{[^} begins a @dfn{complement character set}, which matches any
+character except the ones specified.  Thus, @samp{[^a-z0-9A-Z]}
+matches all characters @emph{except} letters and digits.@refill
+@samp{^} is not special in a character set unless it is the first
+character.  The character following the @samp{^} is treated as if it
+were first (thus, @samp{-} and @samp{]} are not special there).
+Note that a complement character set can match a newline, unless
+newline is mentioned as one of the characters not to match.
+@item ^
+@cindex @samp{^} in regexp
+@cindex beginning of line in regexp
+is a special character that matches the empty string, but only at the
+beginning of a line in the text being matched.  Otherwise it fails to
+match anything.  Thus, @samp{^foo} matches a @samp{foo} that occurs at
+the beginning of a line.
+When matching a string instead of a buffer, @samp{^} matches at the
+beginning of the string or after a newline character @samp{\n}.
+@item $
+@cindex @samp{$} in regexp
+is similar to @samp{^} but matches only at the end of a line.  Thus,
+@samp{x+$} matches a string of one @samp{x} or more at the end of a line.
+When matching a string instead of a buffer, @samp{$} matches at the end
+of the string or before a newline character @samp{\n}.
+@item \
+@cindex @samp{\} in regexp
+has two functions: it quotes the special characters (including
+@samp{\}), and it introduces additional special constructs.
+Because @samp{\} quotes special characters, @samp{\$} is a regular
+expression that matches only @samp{$}, and @samp{\[} is a regular
+expression that matches only @samp{[}, and so on.
+Note that @samp{\} also has special meaning in the read syntax of Lisp
+strings (@pxref{String Type}), and must be quoted with @samp{\}.  For
+example, the regular expression that matches the @samp{\} character is
+@samp{\\}.  To write a Lisp string that contains the characters
+@samp{\\}, Lisp syntax requires you to quote each @samp{\} with another
+@samp{\}.  Therefore, the read syntax for a regular expression matching
+@samp{\} is @code{"\\\\"}.@refill
+@end table
+@strong{Please note:} For historical compatibility, special characters
+are treated as ordinary ones if they are in contexts where their special
+meanings make no sense.  For example, @samp{*foo} treats @samp{*} as
+ordinary since there is no preceding expression on which the @samp{*}
+can act.  It is poor practice to depend on this behavior; quote the
+special character anyway, regardless of where it appears.@refill
+For the most part, @samp{\} followed by any character matches only
+that character.  However, there are several exceptions: characters
+that, when preceded by @samp{\}, are special constructs.  Such
+characters are always ordinary when encountered on their own.  Here
+is a table of @samp{\} constructs:
+@table @kbd
+@item \|
+@cindex @samp{|} in regexp
+@cindex regexp alternative
+specifies an alternative.
+Two regular expressions @var{a} and @var{b} with @samp{\|} in
+between form an expression that matches anything that either @var{a} or
+@var{b} matches.@refill
+Thus, @samp{foo\|bar} matches either @samp{foo} or @samp{bar}
+but no other string.@refill
+@samp{\|} applies to the largest possible surrounding expressions.  Only a
+surrounding @samp{\( @dots{} \)} grouping can limit the grouping power of
+@samp{\|}.@refill
+Full backtracking capability exists to handle multiple uses of @samp{\|}.
+@item \( @dots{} \)
+@cindex @samp{(} in regexp
+@cindex @samp{)} in regexp
+@cindex regexp grouping
+is a grouping construct that serves three purposes:
+@enumerate
+@item
+To enclose a set of @samp{\|} alternatives for other operations.
+Thus, @samp{\(foo\|bar\)x} matches either @samp{foox} or @samp{barx}.
+@item
+To enclose an expression for a suffix operator such as @samp{*} to act
+on.  Thus, @samp{ba\(na\)*} matches @samp{bananana}, etc., with any
+(zero or more) number of @samp{na} strings.@refill
+@item
+To record a matched substring for future reference.
+@end enumerate
+This last application is not a consequence of the idea of a
+parenthetical grouping; it is a separate feature that happens to be
+assigned as a second meaning to the same @samp{\( @dots{} \)} construct
+because there is no conflict in practice between the two meanings.
+Here is an explanation of this feature:
+@item \@var{digit}
+matches the same text that matched the @var{digit}th occurrence of a
+@samp{\( @dots{} \)} construct.
+In other words, after the end of a @samp{\( @dots{} \)} construct.  the
+matcher remembers the beginning and end of the text matched by that
+construct.  Then, later on in the regular expression, you can use
+@samp{\} followed by @var{digit} to match that same text, whatever it
+may have been.
+The strings matching the first nine @samp{\( @dots{} \)} constructs
+appearing in a regular expression are assigned numbers 1 through 9 in
+the order that the open parentheses appear in the regular expression.
+So you can use @samp{\1} through @samp{\9} to refer to the text matched
+by the corresponding @samp{\( @dots{} \)} constructs.
+For example, @samp{\(.*\)\1} matches any newline-free string that is
+composed of two identical halves.  The @samp{\(.*\)} matches the first
+half, which may be anything, but the @samp{\1} that follows must match
+the same exact text.
+@item \(?: @dots{} \)
+@cindex @samp{\(?:} in regexp
+@cindex regexp grouping
+is called a @dfn{shy} grouping operator, and it is used just like
+@samp{\( @dots{} \)}, except that it does not cause the matched
+substring to be recorded for future reference.
+This is useful when you need a lot of grouping @samp{\( @dots{} \)}
+constructs, but only want to remember one or two.  Then you can use
+not want to remember them for later use with @code{match-string}.
+Using @samp{\(?: @dots{} \)} rather than @samp{\( @dots{} \)} when you
+don't need the captured substrings ought to speed up your programs some,
+since it shortens the code path followed by the regular expression
+engine, as well as the amount of memory allocation and string copying it
+must do.  The actual performance gain to be observed has not been
+measured or quantified as of this writing.
+@c This is used to good advantage by the font-locking code, and by
+@c `regexp-opt.el'.  ... It will be.  It's not yet, but will be.
+The shy grouping operator has been borrowed from Perl, and has not been
+available prior to XEmacs 20.3, nor is it available in FSF Emacs.
+@item \w
+@cindex @samp{\w} in regexp
+matches any word-constituent character.  The editor syntax table
+determines which characters these are.  @xref{Syntax Tables}.
+@item \W
+@cindex @samp{\W} in regexp
+matches any character that is not a word constituent.
+@item \s@var{code}
+@cindex @samp{\s} in regexp
+matches any character whose syntax is @var{code}.  Here @var{code} is a
+character that represents a syntax code: thus, @samp{w} for word
+constituent, @samp{-} for whitespace, @samp{(} for open parenthesis,
+etc.  @xref{Syntax Tables}, for a list of syntax codes and the
+characters that stand for them.
+@item \S@var{code}
+@cindex @samp{\S} in regexp
+matches any character whose syntax is not @var{code}.
+@end table
+The following regular expression constructs match the empty string---that is,
+they don't use up any characters---but whether they match depends on the
+context.
+@table @kbd
+@item \`
+@cindex @samp{\`} in regexp
+matches the empty string, but only at the beginning
+of the buffer or string being matched against.
+@item \'
+@cindex @samp{\'} in regexp
+matches the empty string, but only at the end of
+the buffer or string being matched against.
+@item \=
+@cindex @samp{\=} in regexp
+matches the empty string, but only at point.
+(This construct is not defined when matching against a string.)
+@item \b
+@cindex @samp{\b} in regexp
+matches the empty string, but only at the beginning or
+end of a word.  Thus, @samp{\bfoo\b} matches any occurrence of
+@samp{foo} as a separate word.  @samp{\bballs?\b} matches
+@samp{ball} or @samp{balls} as a separate word.@refill
+@item \B
+@cindex @samp{\B} in regexp
+matches the empty string, but @emph{not} at the beginning or
+end of a word.
+@item \<
+@cindex @samp{\<} in regexp
+matches the empty string, but only at the beginning of a word.
+@item \>
+@cindex @samp{\>} in regexp
+matches the empty string, but only at the end of a word.
+@end table
+@kindex invalid-regexp
+Not every string is a valid regular expression.  For example, a string
+with unbalanced square brackets is invalid (with a few exceptions, such
+as @samp{[]]}), and so is a string that ends with a single @samp{\}.  If
+an invalid regular expression is passed to any of the search functions,
+an @code{invalid-regexp} error is signaled.
+@defun regexp-quote string
+This function returns a regular expression string that matches exactly
+@var{string} and nothing else.  This allows you to request an exact
+string match when calling a function that wants a regular expression.
+@example
+@group
+(regexp-quote "^The cat$")
+@result{} "\\^The cat\\$"
+@end group
+@end example
+One use of @code{regexp-quote} is to combine an exact string match with
+context described as a regular expression.  For example, this searches
+for the string that is the value of @code{string}, surrounded by
+whitespace:
+@example
+@group
+(re-search-forward
+(concat "\\s-" (regexp-quote string) "\\s-"))
+@end group
+@end example
+@end defun
+@node Regexp Example
+@subsection Complex Regexp Example
+Here is a complicated regexp, used by XEmacs to recognize the end of a
+sentence together with any whitespace that follows.  It is the value of
+the variable @code{sentence-end}.
+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
+double-quote.  @samp{\"} stands for a double-quote as part of the
+string, @samp{\\} for a backslash as part of the string, @samp{\t} for a
+tab and @samp{\n} for a newline.
+@example
+"[.?!][]\"')@}]*\\($\\| $\\|\t\\|  \\)[ \t\n]*"
+@end example
+In contrast, if you evaluate the variable @code{sentence-end}, you
+will see the following:
+@example
+@group
+sentence-end
+@result{}
+"[.?!][]\"')@}]*\\($\\| $\\|  \\|  \\)[
+]*"
+@end group
+@end example
+@noindent
+In this output, tab and newline appear as themselves.
+This regular expression contains four parts in succession and can be
+deciphered as follows:
+@table @code
+@item [.?!]
+The first part of the pattern is a character set that matches any one of
+three characters: period, question mark, and exclamation mark.  The
+match must begin with one of these three characters.
+@item []\"')@}]*
+The second part of the pattern matches any closing braces and quotation
+marks, zero or more of them, that may follow the period, question mark
+or exclamation mark.  The @code{\"} is Lisp syntax for a double-quote in
+a string.  The @samp{*} at the end indicates that the immediately
+preceding regular expression (a character set, in this case) may be
+repeated zero or more times.
+@item \\($\\|@ $\\|\t\\|@ @ \\)
+The third part of the pattern matches the whitespace that follows the
+end of a sentence: the end of a line, or a tab, or two spaces.  The
+double backslashes mark the parentheses and vertical bars as regular
+expression syntax; the parentheses delimit a group and the vertical bars
+separate alternatives.  The dollar sign is used to match the end of a
+line.
+@item [ \t\n]*
+Finally, the last part of the pattern matches any additional whitespace
+beyond the minimum needed to end a sentence.
+@end table
+@node Regexp Search
+@section Regular Expression Searching
+@cindex regular expression searching
+@cindex regexp searching
+@cindex searching for regexp
+In XEmacs, you can search for the next match for a regexp either
+incrementally or not.  Incremental search commands are described in the
+@cite{The XEmacs Reference Manual}.  @xref{Regexp Search, , Regular Expression
+Search, emacs, The XEmacs Reference Manual}.  Here we describe only the search
+functions useful in programs.  The principal one is
+@code{re-search-forward}.
+@deffn Command re-search-forward regexp &optional limit noerror repeat
+This function searches forward in the current buffer for a string of
+text that is matched by the regular expression @var{regexp}.  The
+function skips over any amount of text that is not matched by
+@var{regexp}, and leaves point at the end of the first match found.
+It returns the new value of point.
+If @var{limit} is non-@code{nil} (it must be a position in the current
+buffer), then it is the upper bound to the search.  No match extending
+after that position is accepted.
+What happens when the search fails depends on the value of
+@var{noerror}.  If @var{noerror} is @code{nil}, a @code{search-failed}
+error is signaled.  If @var{noerror} is @code{t},
+@code{re-search-forward} does nothing and returns @code{nil}.  If
+@var{noerror} is neither @code{nil} nor @code{t}, then
+@code{re-search-forward} moves point to @var{limit} (or the end of the
+buffer) and returns @code{nil}.
+If @var{repeat} is supplied (it must be a positive number), then the
+search is repeated that many times (each time starting at the end of the
+previous time's match).  If these successive searches succeed, the
+function succeeds, moving point and returning its new value.  Otherwise
+the search fails.
+In the following example, point is initially before the @samp{T}.
+Evaluating the search call moves point to the end of that line (between
+the @samp{t} of @samp{hat} and the newline).
+@example
+@group
+---------- Buffer: foo ----------
+I read "@point{}The cat in the hat
+comes back" twice.
+---------- Buffer: foo ----------
+@end group
+@group
+(re-search-forward "[a-z]+" nil t 5)
+@result{} 27
+---------- Buffer: foo ----------
+I read "The cat in the hat@point{}
+comes back" twice.
+---------- Buffer: foo ----------
+@end group
+@end example
+@end deffn
+@deffn Command re-search-backward regexp &optional limit noerror repeat
+This function searches backward in the current buffer for a string of
+text that is matched by the regular expression @var{regexp}, leaving
+point at the beginning of the first text found.
+This function is analogous to @code{re-search-forward}, but they are not
+simple mirror images.  @code{re-search-forward} finds the match whose
+beginning is as close as possible to the starting point.  If
+@code{re-search-backward} were a perfect mirror image, it would find the
+match whose end is as close as possible.  However, in fact it finds the
+match whose beginning is as close as possible.  The reason is that
+matching a regular expression at a given spot always works from
+beginning to end, and starts at a specified beginning position.
+A true mirror-image of @code{re-search-forward} would require a special
+feature for matching regexps from end to beginning.  It's not worth the
+trouble of implementing that.
+@end deffn
+@defun string-match regexp string &optional start
+This function returns the index of the start of the first match for
+the regular expression @var{regexp} in @var{string}, or @code{nil} if
+there is no match.  If @var{start} is non-@code{nil}, the search starts
+at that index in @var{string}.
+For example,
+@example
+@group
+(string-match
+"quick" "The quick brown fox jumped quickly.")
+@result{} 4
+@end group
+@group
+(string-match
+"quick" "The quick brown fox jumped quickly." 8)
+@result{} 27
+@end group
+@end example
+@noindent
+The index of the first character of the
+string is 0, the index of the second character is 1, and so on.
+After this function returns, the index of the first character beyond
+the match is available as @code{(match-end 0)}.  @xref{Match Data}.
+@example
+@group
+(string-match
+"quick" "The quick brown fox jumped quickly." 8)
+@result{} 27
+@end group
+@group
+(match-end 0)
+@result{} 32
+@end group
+@end example
+@end defun
+@defun split-string string &optional pattern
+This function splits @var{string} to substrings delimited by
+@var{pattern}, and returns a list of substrings.  If @var{pattern} is
+omitted, it defaults to @samp{[ \f\t\n\r\v]+}, which means that it
+splits @var{string} by white--space.
+@example
+@group
+(split-string "foo bar")
+@result{} ("foo" "bar")
+@end group
+@group
+(split-string "something")
+@result{} ("something")
+@end group
+@group
+(split-string "a:b:c" ":")
+@result{} ("a" "b" "c")
+@end group
+@group
+(split-string ":a::b:c" ":")
+@result{} ("" "a" "" "b" "c")
+@end group
+@end example
+@end defun
+@defun split-path path
+This function splits a search path into a list of strings.  The path
+components are separated with the characters specified with
+@code{path-separator}.  Under Unix, @code{path-separator} will normally
+be @samp{:}, while under Windows, it will be @samp{;}.
+@end defun
+@defun looking-at regexp
+This function determines whether the text in the current buffer directly
+following point matches the regular expression @var{regexp}.  ``Directly
+following'' means precisely that: the search is ``anchored'' and it can
+succeed only starting with the first character following point.  The
+result is @code{t} if so, @code{nil} otherwise.
+This function does not move point, but it updates the match data, which
+you can access using @code{match-beginning} and @code{match-end}.
+@xref{Match Data}.
+In this example, point is located directly before the @samp{T}.  If it
+were anywhere else, the result would be @code{nil}.
+@example
+@group
+---------- Buffer: foo ----------
+I read "@point{}The cat in the hat
+comes back" twice.
+---------- Buffer: foo ----------
+(looking-at "The cat in the hat$")
+@result{} t
+@end group
+@end example
+@end defun
+@node POSIX Regexps
+@section POSIX Regular Expression Searching
+The usual regular expression functions do backtracking when necessary
+to handle the @samp{\|} and repetition constructs, but they continue
+this only until they find @emph{some} match.  Then they succeed and
+report the first match found.
+This section describes alternative search functions which perform the
+full backtracking specified by the POSIX standard for regular expression
+matching.  They continue backtracking until they have tried all
+possibilities and found all matches, so they can report the longest
+match, as required by POSIX.  This is much slower, so use these
+functions only when you really need the longest match.
+In Emacs versions prior to 19.29, these functions did not exist, and
+the functions described above implemented full POSIX backtracking.
+@defun posix-search-forward regexp &optional limit noerror repeat
+This is like @code{re-search-forward} except that it performs the full
+backtracking specified by the POSIX standard for regular expression
+matching.
+@end defun
+@defun posix-search-backward regexp &optional limit noerror repeat
+This is like @code{re-search-backward} except that it performs the full
+backtracking specified by the POSIX standard for regular expression
+matching.
+@end defun
+@defun posix-looking-at regexp
+This is like @code{looking-at} except that it performs the full
+backtracking specified by the POSIX standard for regular expression
+matching.
+@end defun
+@defun posix-string-match regexp string &optional start
+This is like @code{string-match} except that it performs the full
+backtracking specified by the POSIX standard for regular expression
+matching.
+@end defun
+@ignore
+@deffn Command delete-matching-lines regexp
+This function is identical to @code{delete-non-matching-lines}, save
+that it deletes what @code{delete-non-matching-lines} keeps.
+In the example below, point is located on the first line of text.
+@example
+@group
+---------- Buffer: foo ----------
+We hold these truths
+to be self-evident,
+that all men are created
+equal, and that they are
+---------- Buffer: foo ----------
+@end group
+@group
+(delete-matching-lines "the")
+@result{} nil
+---------- Buffer: foo ----------
+to be self-evident,
+that all men are created
+---------- Buffer: foo ----------
+@end group
+@end example
+@end deffn
+@deffn Command flush-lines regexp
+This function is the same as @code{delete-matching-lines}.
+@end deffn
+@defun delete-non-matching-lines regexp
+This function deletes all lines following point which don't
+contain a match for the regular expression @var{regexp}.
+@end defun
+@deffn Command keep-lines regexp
+This function is the same as @code{delete-non-matching-lines}.
+@end deffn
+@deffn Command how-many regexp
+This function counts the number of matches for @var{regexp} there are in
+the current buffer following point.  It prints this number in
+the echo area, returning the string printed.
+@end deffn
+@deffn Command count-matches regexp
+This function is a synonym of @code{how-many}.
+@end deffn
+@deffn Command list-matching-lines regexp nlines
+This function is a synonym of @code{occur}.
+Show all lines following point containing a match for @var{regexp}.
+Display each line with @var{nlines} lines before and after,
+or @code{-}@var{nlines} before if @var{nlines} is negative.
+@var{nlines} defaults to @code{list-matching-lines-default-context-lines}.
+Interactively it is the prefix arg.
+The lines are shown in a buffer named @samp{*Occur*}.
+It serves as a menu to find any of the occurrences in this buffer.
+@kbd{C-h m} (@code{describe-mode} in that buffer gives help.
+@end deffn
+@defopt list-matching-lines-default-context-lines
+Default value is 0.
+Default number of context lines to include around a @code{list-matching-lines}
+match.  A negative number means to include that many lines before the match.
+A positive number means to include that many lines both before and after.
+@end defopt
+@end ignore
+@node Search and Replace
+@section Search and Replace
+@cindex replacement
+@defun perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map
+This function is the guts of @code{query-replace} and related commands.
+It searches for occurrences of @var{from-string} and replaces some or
+all of them.  If @var{query-flag} is @code{nil}, it replaces all
+occurrences; otherwise, it asks the user what to do about each one.
+If @var{regexp-flag} is non-@code{nil}, then @var{from-string} is
+considered a regular expression; otherwise, it must match literally.  If
+@var{delimited-flag} is non-@code{nil}, then only replacements
+surrounded by word boundaries are considered.
+The argument @var{replacements} specifies what to replace occurrences
+with.  If it is a string, that string is used.  It can also be a list of
+strings, to be used in cyclic order.
+If @var{repeat-count} is non-@code{nil}, it should be an integer.  Then
+it specifies how many times to use each of the strings in the
+@var{replacements} list before advancing cyclicly to the next one.
+Normally, the keymap @code{query-replace-map} defines the possible user
+responses for queries.  The argument @var{map}, if non-@code{nil}, is a
+keymap to use instead of @code{query-replace-map}.
+@end defun
+@defvar query-replace-map
+This variable holds a special keymap that defines the valid user
+responses for @code{query-replace} and related functions, as well as
+@code{y-or-n-p} and @code{map-y-or-n-p}.  It is unusual in two ways:
+@itemize @bullet
+@item
+The ``key bindings'' are not commands, just symbols that are meaningful
+to the functions that use this map.
+@item
+Prefix keys are not supported; each key binding must be for a single event
+key sequence.  This is because the functions don't use read key sequence to
+get the input; instead, they read a single event and look it up ``by hand.''
+@end itemize
+@end defvar
+Here are the meaningful ``bindings'' for @code{query-replace-map}.
+Several of them are meaningful only for @code{query-replace} and
+friends.
+@table @code
+@item act
+Do take the action being considered---in other words, ``yes.''
+@item skip
+Do not take action for this question---in other words, ``no.''
+@item exit
+Answer this question ``no,'' and give up on the entire series of
+questions, assuming that the answers will be ``no.''
+@item act-and-exit
+Answer this question ``yes,'' and give up on the entire series of
+questions, assuming that subsequent answers will be ``no.''
+@item act-and-show
+Answer this question ``yes,'' but show the results---don't advance yet
+to the next question.
+@item automatic
+Answer this question and all subsequent questions in the series with
+``yes,'' without further user interaction.
+@item backup
+Move back to the previous place that a question was asked about.
+@item edit
+Enter a recursive edit to deal with this question---instead of any
+other action that would normally be taken.
+@item delete-and-edit
+Delete the text being considered, then enter a recursive edit to replace
+it.
+@item recenter
+Redisplay and center the window, then ask the same question again.
+@item quit
+Perform a quit right away.  Only @code{y-or-n-p} and related functions
+use this answer.
+@item help
+Display some help, then ask again.
+@end table
+@node Match Data
+@section The Match Data
+@cindex match data
+XEmacs keeps track of the positions of the start and end of segments of
+text found during a regular expression search.  This means, for example,
+that you can search for a complex pattern, such as a date in an Rmail
+message, and then extract parts of the match under control of the
+pattern.
+Because the match data normally describe the most recent search only,
+you must be careful not to do another search inadvertently between the
+search you wish to refer back to and the use of the match data.  If you
+can't avoid another intervening search, you must save and restore the
+match data around it, to prevent it from being overwritten.
+@menu
+* Simple Match Data::     Accessing single items of match data,
+			    such as where a particular subexpression started.
+* Replacing Match::	  Replacing a substring that was matched.
+* Entire Match Data::     Accessing the entire match data at once, as a list.
+* Saving Match Data::     Saving and restoring the match data.
+@end menu
+@node Simple Match Data
+@subsection Simple Match Data Access
+This section explains how to use the match data to find out what was
+matched by the last search or match operation.
+You can ask about the entire matching text, or about a particular
+parenthetical subexpression of a regular expression.  The @var{count}
+argument in the functions below specifies which.  If @var{count} is
+zero, you are asking about the entire match.  If @var{count} is
+positive, it specifies which subexpression you want.
+Recall that the subexpressions of a regular expression are those
+expressions grouped with escaped parentheses, @samp{\(@dots{}\)}.  The
+@var{count}th subexpression is found by counting occurrences of
+@samp{\(} from the beginning of the whole regular expression.  The first
+subexpression is numbered 1, the second 2, and so on.  Only regular
+expressions can have subexpressions---after a simple string search, the
+only information available is about the entire match.
+@defun match-string count &optional in-string
+This function returns, as a string, the text matched in the last search
+or match operation.  It returns the entire text if @var{count} is zero,
+or just the portion corresponding to the @var{count}th parenthetical
+subexpression, if @var{count} is positive.  If @var{count} is out of
+range, or if that subexpression didn't match anything, the value is
+@code{nil}.
+If the last such operation was done against a string with
+@code{string-match}, then you should pass the same string as the
+argument @var{in-string}.  Otherwise, after a buffer search or match,
+you should omit @var{in-string} or pass @code{nil} for it; but you
+should make sure that the current buffer when you call
+@code{match-string} is the one in which you did the searching or
+matching.
+@end defun
+@defun match-beginning count
+This function returns the position of the start of text matched by the
+last regular expression searched for, or a subexpression of it.
+If @var{count} is zero, then the value is the position of the start of
+the entire match.  Otherwise, @var{count} specifies a subexpression in
+the regular expression, and the value of the function is the starting
+position of the match for that subexpression.
+The value is @code{nil} for a subexpression inside a @samp{\|}
+alternative that wasn't used in the match.
+@end defun
+@defun match-end count
+This function is like @code{match-beginning} except that it returns the
+position of the end of the match, rather than the position of the
+beginning.
+@end defun
+Here is an example of using the match data, with a comment showing the
+positions within the text:
+@example
+@group
+(string-match "\\(qu\\)\\(ick\\)"
+"The quick fox jumped quickly.")
+;0123456789
+@result{} 4
+@end group
+@group
+(match-string 0 "The quick fox jumped quickly.")
+@result{} "quick"
+(match-string 1 "The quick fox jumped quickly.")
+@result{} "qu"
+(match-string 2 "The quick fox jumped quickly.")
+@result{} "ick"
+@end group
+@group
+(match-beginning 1)       ; @r{The beginning of the match}
+@result{} 4                 ;   @r{with @samp{qu} is at index 4.}
+@end group
+@group
+(match-beginning 2)       ; @r{The beginning of the match}
+@result{} 6                 ;   @r{with @samp{ick} is at index 6.}
+@end group
+@group
+(match-end 1)             ; @r{The end of the match}
+@result{} 6                 ;   @r{with @samp{qu} is at index 6.}
+(match-end 2)             ; @r{The end of the match}
+@result{} 9                 ;   @r{with @samp{ick} is at index 9.}
+@end group
+@end example
+Here is another example.  Point is initially located at the beginning
+of the line.  Searching moves point to between the space and the word
+@samp{in}.  The beginning of the entire match is at the 9th character of
+the buffer (@samp{T}), and the beginning of the match for the first
+subexpression is at the 13th character (@samp{c}).
+@example
+@group
+(list
+(re-search-forward "The \\(cat \\)")
+(match-beginning 0)
+(match-beginning 1))
+@result{} (9 9 13)
+@end group
+@group
+---------- Buffer: foo ----------
+I read "The cat @point{}in the hat comes back" twice.
+^   ^
+9  13
+---------- Buffer: foo ----------
+@end group
+@end example
+@noindent
+(In this case, the index returned is a buffer position; the first
+character of the buffer counts as 1.)
+@node Replacing Match
+@subsection Replacing the Text That Matched
+This function replaces the text matched by the last search with
+@var{replacement}.
+@cindex case in replacements
+@defun replace-match replacement &optional fixedcase literal string
+This function replaces the text in the buffer (or in @var{string}) that
+was matched by the last search.  It replaces that text with
+@var{replacement}.
+If you did the last search in a buffer, you should specify @code{nil}
+for @var{string}.  Then @code{replace-match} does the replacement by
+editing the buffer; it leaves point at the end of the replacement text,
+and returns @code{t}.
+If you did the search in a string, pass the same string as @var{string}.
+Then @code{replace-match} does the replacement by constructing and
+returning a new string.
+If @var{fixedcase} is non-@code{nil}, then the case of the replacement
+text is not changed; otherwise, the replacement text is converted to a
+different case depending upon the capitalization of the text to be
+replaced.  If the original text is all upper case, the replacement text
+is converted to upper case.  If the first word of the original text is
+capitalized, then the first word of the replacement text is capitalized.
+If the original text contains just one word, and that word is a capital
+letter, @code{replace-match} considers this a capitalized first word
+rather than all upper case.
+If @code{case-replace} is @code{nil}, then case conversion is not done,
+regardless of the value of @var{fixed-case}.  @xref{Searching and Case}.
+If @var{literal} is non-@code{nil}, then @var{replacement} is inserted
+exactly as it is, the only alterations being case changes as needed.
+If it is @code{nil} (the default), then the character @samp{\} is treated
+specially.  If a @samp{\} appears in @var{replacement}, then it must be
+part of one of the following sequences:
+@table @asis
+@item @samp{\&}
+@cindex @samp{&} in replacement
+@samp{\&} stands for the entire text being replaced.
+@item @samp{\@var{n}}
+@cindex @samp{\@var{n}} in replacement
+@samp{\@var{n}}, where @var{n} is a digit, stands for the text that
+matched the @var{n}th subexpression in the original regexp.
+Subexpressions are those expressions grouped inside @samp{\(@dots{}\)}.
+@item @samp{\\}
+@cindex @samp{\} in replacement
+@samp{\\} stands for a single @samp{\} in the replacement text.
+@end table
+@end defun
+@node Entire Match Data
+@subsection Accessing the Entire Match Data
+The functions @code{match-data} and @code{set-match-data} read or
+write the entire match data, all at once.
+@defun match-data
+This function returns a newly constructed list containing all the
+information on what text the last search matched.  Element zero is the
+position of the beginning of the match for the whole expression; element
+one is the position of the end of the match for the expression.  The
+next two elements are the positions of the beginning and end of the
+match for the first subexpression, and so on.  In general, element
+@ifinfo
+number 2@var{n}
+@end ifinfo
+@tex
+number {\mathsurround=0pt $2n$}
+@end tex
+corresponds to @code{(match-beginning @var{n})}; and
+element
+@ifinfo
+number 2@var{n} + 1
+@end ifinfo
+@tex
+number {\mathsurround=0pt $2n+1$}
+@end tex
+corresponds to @code{(match-end @var{n})}.
+All the elements are markers or @code{nil} if matching was done on a
+buffer, and all are integers or @code{nil} if matching was done on a
+string with @code{string-match}.  (In Emacs 18 and earlier versions,
+markers were used even for matching on a string, except in the case
+of the integer 0.)
+As always, there must be no possibility of intervening searches between
+the call to a search function and the call to @code{match-data} that is
+intended to access the match data for that search.
+@example
+@group
+(match-data)
+@result{}  (#<marker at 9 in foo>
+#<marker at 17 in foo>
+#<marker at 13 in foo>
+#<marker at 17 in foo>)
+@end group
+@end example
+@end defun
+@defun set-match-data match-list
+This function sets the match data from the elements of @var{match-list},
+which should be a list that was the value of a previous call to
+@code{match-data}.
+If @var{match-list} refers to a buffer that doesn't exist, you don't get
+an error; that sets the match data in a meaningless but harmless way.
+@findex store-match-data
+@code{store-match-data} is an alias for @code{set-match-data}.
+@end defun
+@node Saving Match Data
+@subsection Saving and Restoring the Match Data
+When you call a function that may do a search, you may need to save
+and restore the match data around that call, if you want to preserve the
+match data from an earlier search for later use.  Here is an example
+that shows the problem that arises if you fail to save the match data:
+@example
+@group
+(re-search-forward "The \\(cat \\)")
+@result{} 48
+(foo)                   ; @r{Perhaps @code{foo} does}
+;   @r{more searching.}
+(match-end 0)
+@result{} 61              ; @r{Unexpected result---not 48!}
+@end group
+@end example
+You can save and restore the match data with @code{save-match-data}:
+@defmac save-match-data body@dots{}
+This special form executes @var{body}, saving and restoring the match
+data around it.
+@end defmac
+You can use @code{set-match-data} together with @code{match-data} to
+imitate the effect of the special form @code{save-match-data}.  This is
+useful for writing code that can run in Emacs 18.  Here is how:
+@example
+@group
+(let ((data (match-data)))
+(unwind-protect
+@dots{}   ; @r{May change the original match data.}
+(set-match-data data)))
+@end group
+@end example
+Emacs automatically saves and restores the match data when it runs
+process filter functions (@pxref{Filter Functions}) and process
+sentinels (@pxref{Sentinels}).
+@ignore
+Here is a function which restores the match data provided the buffer
+associated with it still exists.
+@smallexample
+@group
+(defun restore-match-data (data)
+@c It is incorrect to split the first line of a doc string.
+@c If there's a problem here, it should be solved in some other way.
+"Restore the match data DATA unless the buffer is missing."
+(catch 'foo
+(let ((d data))
+@end group
+(while d
+(and (car d)
+(null (marker-buffer (car d)))
+@group
+;; @file{match-data} @r{buffer is deleted.}
+(throw 'foo nil))
+(setq d (cdr d)))
+(set-match-data data))))
+@end group
+@end smallexample
+@end ignore
+@node Searching and Case
+@section Searching and Case
+@cindex searching and case
+By default, searches in Emacs ignore the case of the text they are
+searching through; if you specify searching for @samp{FOO}, then
+@samp{Foo} or @samp{foo} is also considered a match.  Regexps, and in
+particular character sets, are included: thus, @samp{[aB]} would match
+@samp{a} or @samp{A} or @samp{b} or @samp{B}.
+If you do not want this feature, set the variable
+@code{case-fold-search} to @code{nil}.  Then all letters must match
+exactly, including case.  This is a buffer-local variable; altering the
+variable affects only the current buffer.  (@xref{Intro to
+Buffer-Local}.)  Alternatively, you may change the value of
+@code{default-case-fold-search}, which is the default value of
+@code{case-fold-search} for buffers that do not override it.
+Note that the user-level incremental search feature handles case
+distinctions differently.  When given a lower case letter, it looks for
+a match of either case, but when given an upper case letter, it looks
+for an upper case letter only.  But this has nothing to do with the
+searching functions Lisp functions use.
+@defopt case-replace
+This variable determines whether the replacement functions should
+preserve case.  If the variable is @code{nil}, that means to use the
+replacement text verbatim.  A non-@code{nil} value means to convert the
+case of the replacement text according to the text being replaced.
+The function @code{replace-match} is where this variable actually has
+its effect.  @xref{Replacing Match}.
+@end defopt
+@defopt case-fold-search
+This buffer-local variable determines whether searches should ignore
+case.  If the variable is @code{nil} they do not ignore case; otherwise
+they do ignore case.
+@end defopt
+@defvar default-case-fold-search
+The value of this variable is the default value for
+@code{case-fold-search} in buffers that do not override it.  This is the
+same as @code{(default-value 'case-fold-search)}.
+@end defvar
+@node Standard Regexps
+@section Standard Regular Expressions Used in Editing
+@cindex regexps used standardly in editing
+@cindex standard regexps used in editing
+This section describes some variables that hold regular expressions
+used for certain purposes in editing:
+@defvar page-delimiter
+This is the regexp describing line-beginnings that separate pages.  The
+default value is @code{"^\014"} (i.e., @code{"^^L"} or @code{"^\C-l"});
+this matches a line that starts with a formfeed character.
+@end defvar
+The following two regular expressions should @emph{not} assume the
+match always starts at the beginning of a line; they should not use
+@samp{^} to anchor the match.  Most often, the paragraph commands do
+check for a match only at the beginning of a line, which means that
+@samp{^} would be superfluous.  When there is a nonzero left margin,
+they accept matches that start after the left margin.  In that case, a
+@samp{^} would be incorrect.  However, a @samp{^} is harmless in modes
+where a left margin is never used.
+@defvar paragraph-separate
+This is the regular expression for recognizing the beginning of a line
+that separates paragraphs.  (If you change this, you may have to
+change @code{paragraph-start} also.)  The default value is
+@w{@code{"[@ \t\f]*$"}}, which matches a line that consists entirely of
+spaces, tabs, and form feeds (after its left margin).
+@end defvar
+@defvar paragraph-start
+This is the regular expression for recognizing the beginning of a line
+that starts @emph{or} separates paragraphs.  The default value is
+@w{@code{"[@ \t\n\f]"}}, which matches a line starting with a space, tab,
+newline, or form feed (after its left margin).
+@end defvar
+@defvar sentence-end
+This is the regular expression describing the end of a sentence.  (All
+paragraph boundaries also end sentences, regardless.)  The default value
+is:
+@example
+"[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
+@end example
+This means a period, question mark or exclamation mark, followed
+optionally by a closing parenthetical character, followed by tabs,
+spaces or new lines.
+For a detailed explanation of this regular expression, see @ref{Regexp
+Example}.
+@end defvar

Mercurial > hg > xemacs-beta

comparison man/lispref/searching.texi @ 428:3ecd8885ac67 r21-2-22