@cindex @samp{\S} in regexp
matches any character whose syntax is not @var{code}.
+@cindex category, regexp search for
@item \c@var{c}
matches any character whose category is @var{c}. Here @var{c} is a
character that represents a category: thus, @samp{c} for Chinese
characters or @samp{g} for Greek characters in the standard category
-table.
+table. You can see the list of all the currently defined categories
+with @kbd{M-x describe-categories @key{RET}}. You can also define
+your own categories in addition to the standard ones using the
+@code{define-category} function (@pxref{Categories}).
@item \C@var{c}
matches any character whose category is not @var{c}.
can't avoid another intervening search, you must save and restore the
match data around it, to prevent it from being overwritten.
+ Notice that all functions are allowed to overwrite the match data
+unless they're explicitly documented not to do so. A consequence is
+that functions that are run implictly in the background
+(@pxref{Timers}, and @ref{Idle Timers}) should likely save and restore
+the match data explicitly.
+
@menu
* Replacing Match:: Replacing a substring that was matched.
* Simple Match Data:: Accessing single items of match data,