X-Git-Url: https://code.delx.au/gnu-emacs/blobdiff_plain/9a7e97c6fb5ad76aacf0f75a6b30503f29fddd54..0f9c4a9694078e41e70426e4eae3bbb52cab0d2a:/lispref/searching.texi

diff --git a/lispref/searching.texi b/lispref/searching.texi
index fd0d0e172a..204cfa1d31 100644
--- a/lispref/searching.texi
+++ b/lispref/searching.texi
@@ -1,7 +1,7 @@
 @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   Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002, 2003,
+@c   2004, 2005, 2006 Free Software Foundation, Inc.
 @c See the file elisp.texi for copying conditions.
 @setfilename ../info/searching
 @node Searching and Matching, Syntax Tables, Non-ASCII Characters, Top
@@ -16,18 +16,19 @@ portions of it.
 
 @menu
 * String Search::         Search for an exact match.
+* Searching and Case::    Case-independent or case-significant searching.
 * 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,
                             after a string or regexp search.
-* Searching and Case::    Case-independent or case-significant searching.
+* Search and Replace::	  Commands that loop, searching and replacing.
 * 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}.
+@xref{Skipping Characters}.  To search for changes in character
+properties, see @ref{Property Search}.
 
 @node String Search
 @section Searching for Strings
@@ -86,6 +87,10 @@ upper bound and returns @code{nil}.  (It would be more consistent now to
 return the new position of point in that case, but some existing
 programs may depend on a value of @code{nil}.)
 
+The argument @var{noerror} only affects valid searches which fail to
+find a match.  Invalid arguments cause errors regardless of
+@var{noerror}.
+
 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
@@ -136,9 +141,9 @@ the ball boy@point{}!"
 @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{limit} is non-@code{nil}, it must be a position in the current
+buffer; it specifies 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
@@ -157,6 +162,53 @@ except that it searches backward and normally leaves point at the
 beginning of the match.
 @end deffn
 
+@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.  This applies to
+regular expressions, too; 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 used in Lisp code.
+
+@defopt case-replace
+This variable determines whether the higher level 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.
+
+This variable is used by passing it as an argument to the function
+@code{replace-match}.  @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 Regular Expressions
 @section Regular Expressions
 @cindex regular expression
@@ -167,6 +219,16 @@ 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.
 
+@findex re-builder
+@cindex authoring regular expressions
+  For convenient interactive development of regular expressions, you
+can use the @kbd{M-x re-builder} command.  It provides a convenient
+interface for creating regular expressions, by giving immediate visual
+feedback in a separate buffer.  As you edit the regexp, all its
+matches in the target buffer are highlighted.  Each parenthesized
+sub-expression of the regexp is shown in a distinct face, which makes
+it easier to verify even very complex regexps.
+
 @menu
 * Syntax of Regexps::       Rules for writing regular expressions.
 * Regexp Example::          Illustrates regular expression syntax.
@@ -178,12 +240,15 @@ regexps; the following section says how to search for them.
 
   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{$}, and @samp{\}; no new
-special characters will be defined in the future.  Any other character
-appearing in a regular expression is ordinary, unless a @samp{\}
-precedes it.
+character is a simple regular expression that matches that character
+and nothing else.  The special characters are @samp{.}, @samp{*},
+@samp{+}, @samp{?}, @samp{[}, @samp{^}, @samp{$}, and @samp{\}; no new
+special characters will be defined in the future.  The character
+@samp{]} is special if it ends a character alternative (see later).
+The character @samp{-} is special inside a character alternative.  A
+@samp{[:} and balancing @samp{:]} enclose a character class inside a
+character alternative.  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
@@ -242,18 +307,19 @@ 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 or loop infinitely
-if they use repetition operators inside repetition operators.  For
-example, it could take hours for the regular expression
-@samp{\(x+y*\)*a} to try to match the sequence
-@samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}, before it ultimately
-fails.  Emacs must try each way of grouping the 35 @samp{x}s before
-concluding that none of them can work.  Even worse, @samp{\(x*\)*} can
-match the null string in infinitely many ways, so it causes an
-infinite loop.  To avoid these problems, check nested repetitions
-carefully.
+this choice, the rest of the regexp matches successfully.
+
+@strong{Warning:} Nested repetition operators take a long time,
+or even forever, if they
+lead to ambiguous matching.  For example, trying to match the regular
+expression @samp{\(x+y*\)*a} against the string
+@samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz} could take hours before it
+ultimately fails.  Emacs must try each way of grouping the 35
+@samp{x}s before concluding that none of them can work.  Even worse,
+@samp{\(x*\)*} can match the null string in infinitely many ways, so
+it causes an infinite loop.  To avoid these problems, check nested
+repetitions carefully, to make sure that they do not cause combinatorial
+explosions in backtracking.
 
 @item @samp{+}
 @cindex @samp{+} in regexp
@@ -338,7 +404,7 @@ does match all non-@acronym{ASCII} characters (see below regarding @samp{^}),
 in both multibyte and unibyte representations, because only the
 @acronym{ASCII} characters are excluded.
 
-Starting in Emacs 21, a character alternative can also specify named
+A character alternative can also specify named
 character classes (@pxref{Char Classes}).  This is a POSIX feature whose
 syntax is @samp{[:@var{class}:]}.  Using a character class is equivalent
 to mentioning each of the characters in that class; but the latter is
@@ -347,9 +413,10 @@ different characters.
 
 @item @samp{[^ @dots{} ]}
 @cindex @samp{^} in regexp
-@samp{[^} begins a @dfn{complemented character alternative}, which matches any
-character except the ones specified.  Thus, @samp{[^a-z0-9A-Z]} matches
-all characters @emph{except} letters and digits.
+@samp{[^} begins a @dfn{complemented character alternative}.  This
+matches any character except the ones specified.  Thus,
+@samp{[^a-z0-9A-Z]} matches all characters @emph{except} letters and
+digits.
 
 @samp{^} is not special in a character alternative unless it is the first
 character.  The character following the @samp{^} is treated as if it
@@ -411,16 +478,44 @@ 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
 
+As a @samp{\} is not special inside a character alternative, it can
+never remove the special meaning of @samp{-} or @samp{]}.  So you
+should not quote these characters when they have no special meaning
+either.  This would not clarify anything, since backslashes can
+legitimately precede these characters where they @emph{have} special
+meaning, as in @samp{[^\]} (@code{"[^\\]"} for Lisp string syntax),
+which matches any single character except a backslash.
+
+In practice, most @samp{]} that occur in regular expressions close a
+character alternative and hence are special.  However, occasionally a
+regular expression may try to match a complex pattern of literal
+@samp{[} and @samp{]}.  In such situations, it sometimes may be
+necessary to carefully parse the regexp from the start to determine
+which square brackets enclose a character alternative.  For example,
+@samp{[^][]]} consists of the complemented character alternative
+@samp{[^][]} (which matches any single character that is not a square
+bracket), followed by a literal @samp{]}.
+
+The exact rules are that at the beginning of a regexp, @samp{[} is
+special and @samp{]} not.  This lasts until the first unquoted
+@samp{[}, after which we are in a character alternative; @samp{[} is
+no longer special (except when it starts a character class) but @samp{]}
+is special, unless it immediately follows the special @samp{[} or that
+@samp{[} followed by a @samp{^}.  This lasts until the next special
+@samp{]} that does not end a character class.  This ends the character
+alternative and restores the ordinary syntax of regular expressions;
+an unquoted @samp{[} is special again and a @samp{]} not.
+
 @node Char Classes
 @subsubsection Character Classes
 @cindex character classes in regexp
 
   Here is a table of the classes you can use in a character alternative,
-in Emacs 21, and what they mean:
+and what they mean:
 
 @table @samp
 @item [:ascii:]
-This matches any @acronym{ASCII} (unibyte) character.
+This matches any @acronym{ASCII} character (codes 0--127).
 @item [:alnum:]
 This matches any letter or digit.  (At present, for multibyte
 characters, it matches anything that has word syntax.)
@@ -440,8 +535,10 @@ characters, space, and the delete character.
 @item [:lower:]
 This matches any lower-case letter, as determined by
 the current case table (@pxref{Case Tables}).
+@item [:multibyte:]
+This matches any multibyte character (@pxref{Text Representations}).
 @item [:nonascii:]
-This matches any non-@acronym{ASCII} (multibyte) character.
+This matches any non-@acronym{ASCII} character.
 @item [:print:]
 This matches printing characters---everything except @acronym{ASCII} control
 characters and the delete character.
@@ -451,6 +548,8 @@ characters, it matches anything that has non-word syntax.)
 @item [:space:]
 This matches any character that has whitespace syntax
 (@pxref{Syntax Class Table}).
+@item [:unibyte:]
+This matches any unibyte character (@pxref{Text Representations}).
 @item [:upper:]
 This matches any upper-case letter, as determined by
 the current case table (@pxref{Case Tables}).
@@ -683,8 +782,8 @@ with a symbol-constituent character.
 
 @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
+that ends inside a character alternative without terminating @samp{]}
+is invalid, 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.
 
@@ -694,9 +793,9 @@ an @code{invalid-regexp} error is signaled.
 
   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
@@ -730,9 +829,9 @@ deciphered as follows:
 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
@@ -844,23 +943,26 @@ 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.
+If @var{limit} is non-@code{nil}, it must be a position in the current
+buffer.  It specifies the upper bound to the search.  No match
+extending after that position is accepted.
 
-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 all these successive searches succeed, the
-function succeeds, moving point and returning its new value.  Otherwise
-the function fails.
+If @var{repeat} is supplied, it must be a positive number; the search
+is repeated that many times; each repetition starts at the end of the
+previous match.  If all these successive searches succeed, the search
+succeeds, moving point and returning its new value.  Otherwise the
+search fails.  What @code{re-search-forward} does when the search
+fails depends on the value of @var{noerror}:
 
-What happens when the function 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
-accessible portion of the buffer) and returns @code{nil}.
+@table @asis
+@item @code{nil}
+Signal a @code{search-failed} error.
+@item @code{t}
+Do nothing and return @code{nil}.
+@item anything else
+Move point to @var{limit} (or the end of the accessible portion of the
+buffer) and return @code{nil}.
+@end table
 
 In the following example, point is initially before the @samp{T}.
 Evaluating the search call moves point to the end of that line (between
@@ -975,6 +1077,45 @@ comes back" twice.
 @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
+
+@defvar search-spaces-regexp
+If this variable is non-@code{nil}, it should be a regular expression
+that says how to search for whitespace.  In that case, any group of
+spaces in a regular expression being searched for stands for use of
+this regular expression.  However, spaces inside of constructs such as
+@samp{[@dots{}]} and @samp{*}, @samp{+}, @samp{?} are not affected by
+@code{search-spaces-regexp}.
+
+Since this variable affects all regular expression search and match
+constructs, you should bind it temporarily for as small as possible
+a part of the code.
+@end defvar
+
 @node POSIX Regexps
 @section POSIX Regular Expression Searching
 
@@ -1018,212 +1159,15 @@ 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 &optional 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 start end
-This function is the guts of @code{query-replace} and related
-commands.  It searches for occurrences of @var{from-string} in the
-text between positions @var{start} and @var{end} and replaces some or
-all of them.  If @var{start} is @code{nil} (or omitted), point is used
-instead, and the end of the buffer's accessible portion is used for
-@var{end}.
-
-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{replacements} is a cons cell, @code{(@var{function}
-. @var{data})}, this means to call @var{function} after each match to
-get the replacement text.  This function is called with two arguments:
-@var{data}, and the number of replacements already made.
-
-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 cyclically to the next one.
-
-If @var{from-string} contains upper-case letters, then
-@code{perform-replace} binds @code{case-fold-search} to @code{nil}, and
-it uses the @code{replacements} without altering the case of them.
-
-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}.
-
-@strong{Usage note:} Do not use this function in your own programs
-unless you want to do something very similar to what
-@code{query-replace} does, including setting the mark and possibly
-querying the user.  For most purposes a simple loop like, for
-instance:
-
-@example
-(while (re-search-forward "foo[ \t]+bar" nil t)
-  (replace-match "foobar"))
-@end example
-
-@noindent
-is preferable.  It runs faster and avoids side effects, such as
-setting the mark.  @xref{Replacing Match,, Replacing the Text that
-Matched}, for a description of @code{replace-match}.
-@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
-@code{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
 
   Emacs keeps track of the start and end positions of the segments of
-text found during a 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.
+text found during a search; this is called the @dfn{match data}.
+Thanks to the match data, you can search for a complex pattern, such
+as a date in a mail 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
@@ -1242,8 +1186,8 @@ match data around it, to prevent it from being overwritten.
 @node Replacing Match
 @subsection Replacing the Text that Matched
 
-  This function replaces the text matched by the last search with
-@var{replacement}.
+  This function replaces all or part of the text matched by the last
+search.  It works by means of the match data.
 
 @cindex case in replacements
 @defun replace-match replacement &optional fixedcase literal string subexp
@@ -1325,6 +1269,12 @@ 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.
 
+  Every successful search sets the match data.  Therefore, you should
+query the match data immediately after searching, before calling any
+other function that might perform another search.  Alternatively, you
+may save and restore the match data (@pxref{Saving Match Data}) around
+the call to functions that could perform another search.
+
   A search which fails may or may not alter the match data.  In the
 past, a failing search did not do this, but we may change it in the
 future.  So don't try to rely on the value of the match data after
@@ -1446,13 +1396,14 @@ character of the buffer counts as 1.)
   The functions @code{match-data} and @code{set-match-data} read or
 write the entire match data, all at once.
 
-@defun match-data &optional integers reuse
-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
+@defun match-data &optional integers reuse reseat
+This function returns a list of positions (markers or integers) that
+record 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
 @ifnottex
 number 2@var{n}
 @end ifnottex
@@ -1469,15 +1420,13 @@ 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}.   If @var{integers} is
-non-@code{nil}, then the elements are integers or @code{nil}, even if
-matching was done on a buffer.  In that case, the buffer itself is
-appended as an additional element at the end of the list
-to facilitate complete restoration of the match data.  Also,
-@code{match-beginning} and
-@code{match-end} always return integers or @code{nil}.
+Normally all the elements are markers or @code{nil}, but if
+@var{integers} is non-@code{nil}, that means to use integers instead
+of markers.  (In that case, the buffer itself is appended as an
+additional element at the end of the list, to facilitate complete
+restoration of the match data.)  If the last match was done on a
+string with @code{string-match}, then integers are always used,
+since markers can't point into a string.
 
 If @var{reuse} is non-@code{nil}, it should be a list.  In that case,
 @code{match-data} stores the match data in @var{reuse}.  That is,
@@ -1485,8 +1434,11 @@ If @var{reuse} is non-@code{nil}, it should be a list.  In that case,
 have the right length.  If it is not long enough to contain the match
 data, it is extended.  If it is too long, the length of @var{reuse}
 stays the same, but the elements that were not used are set to
-@code{nil}.  The purpose of this feature is to avoid producing too
-much garbage, that would later have to be collected.
+@code{nil}.  The purpose of this feature is to reduce the need for
+garbage collection.
+
+If @var{reseat} is non-@code{nil}, all markers on the @var{reuse} list
+are reseated to point to nowhere.
 
 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
@@ -1503,7 +1455,7 @@ intended to access the match data for that search.
 @end example
 @end defun
 
-@defun set-match-data match-list
+@defun set-match-data match-list &optional reseat
 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}.  (More precisely, anything that has the same format
@@ -1512,6 +1464,9 @@ will work.)
 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.
 
+If @var{reseat} is non-@code{nil}, all markers on the @var{match-list} list
+are reseated to point to nowhere.
+
 @findex store-match-data
 @code{store-match-data} is a semi-obsolete alias for @code{set-match-data}.
 @end defun
@@ -1585,53 +1540,156 @@ associated with it still exists.
 @end smallexample
 @end ignore
 
-@node Searching and Case
-@section Searching and Case
-@cindex searching and case
+@node Search and Replace
+@section Search and Replace
+@cindex replacement
 
-  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.  This applies to
-regular expressions, too; thus, @samp{[aB]} would match @samp{a} or
-@samp{A} or @samp{b} or @samp{B}.
+  If you want to find all matches for a regexp in part of the buffer,
+and replace them, the best way is to write an explicit loop using
+@code{re-search-forward} and @code{replace-match}, like this:
 
-  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.
+@example
+(while (re-search-forward "foo[ \t]+bar" nil t)
+  (replace-match "foobar"))
+@end example
 
-  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 used in Lisp code.
+@noindent
+@xref{Replacing Match,, Replacing the Text that Matched}, for a
+description of @code{replace-match}.
+
+  However, replacing matches in a string is more complex, especially
+if you want to do it efficiently.  So Emacs provides a function to do
+this.
+
+@defun replace-regexp-in-string regexp rep string &optional fixedcase literal subexp start
+This function copies @var{string} and searches it for matches for
+@var{regexp}, and replaces them with @var{rep}.  It returns the
+modified copy.  If @var{start} is non-@code{nil}, the search for
+matches starts at that index in @var{string}, so matches starting
+before that index are not changed.
+
+This function uses @code{replace-match} to do the replacement, and it
+passes the optional arguments @var{fixedcase}, @var{literal} and
+@var{subexp} along to @code{replace-match}.
+
+Instead of a string, @var{rep} can be a function.  In that case,
+@code{replace-regexp-in-string} calls @var{rep} for each match,
+passing the text of the match as its sole argument.  It collects the
+value @var{rep} returns and passes that to @code{replace-match} as the
+replacement string.  The match-data at this point are the result
+of matching @var{regexp} against a substring of @var{string}.
+@end defun
 
-@defopt case-replace
-This variable determines whether the higher level 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.
+  If you want to write a command along the lines of @code{query-replace},
+you can use @code{perform-replace} to do the work.
 
-This variable is used by passing it as an argument to the function
-@code{replace-match}.  @xref{Replacing Match}.
-@end defopt
+@defun perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map start end
+This function is the guts of @code{query-replace} and related
+commands.  It searches for occurrences of @var{from-string} in the
+text between positions @var{start} and @var{end} and replaces some or
+all of them.  If @var{start} is @code{nil} (or omitted), point is used
+instead, and the end of the buffer's accessible portion is used for
+@var{end}.
 
-@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
+If @var{query-flag} is @code{nil}, it replaces all
+occurrences; otherwise, it asks the user what to do about each one.
 
-@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)}.
+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{replacements} is a cons cell, @code{(@var{function}
+. @var{data})}, this means to call @var{function} after each match to
+get the replacement text.  This function is called with two arguments:
+@var{data}, and the number of replacements already made.
+
+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 cyclically to the next one.
+
+If @var{from-string} contains upper-case letters, then
+@code{perform-replace} binds @code{case-fold-search} to @code{nil}, and
+it uses the @code{replacements} without altering the case of them.
+
+Normally, the keymap @code{query-replace-map} defines the possible
+user responses for queries.  The argument @var{map}, if
+non-@code{nil}, specifies 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{perform-replace} and the commands that use it, as
+well as @code{y-or-n-p} and @code{map-y-or-n-p}.  This map 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
+@code{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 Standard Regexps
 @section Standard Regular Expressions Used in Editing
 @cindex regexps used standardly in editing
@@ -1672,23 +1730,25 @@ whitespace or starting with a 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 (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