(Character Sets): Document `map-charset-chars'.

doc/lispref/ChangeLog

@@ -4,6 +4,7 @@
 	paragraph to speak about `undecided'.
 	(Character Properties): Don't explain the meaning of each
 	property; instead, identify their Unicode Standard names.
+	(Character Sets): Document `map-charset-chars'.
 
 2008-12-02  Glenn Morris  <rgm@gnu.org>
 

doc/lispref/nonascii.texi

@@ -626,6 +626,23 @@ integer, it is returned as a cons cell @code{(@var{high} . @var{low})}
 that fits the second argument of @code{decode-char} above.  If
 @var{charset} doesn't have a codepoint for @var{char}, the value is
 @code{nil}.
+@end defun
+
+  The following function comes in handy for applying a certain
+function to all or part of the characters in a charset:
+
+@defun map-charset-chars function charset &optional arg from to
+Call @var{function} for characters in @var{charset}.  @var{function}
+is called with two arguments.  The first one is a cons cell
+@code{(@var{from} .  @var{to})}, where @var{from} and @var{to}
+indicate a range of characters contained in charset.  The second
+argument is the optional argument @var{arg}.
+
+By default, the range of codepoints passed to @var{function} includes
+all the characters in @var{charset}, but optional arguments @var{from}
+and @var{to} limit that to the range of characters between these two
+codepoints.  If either of them is @code{nil}, it defaults to the first
+or last codepoint of @var{charset}, respectively.
 @end defun
 
 @node Scanning Charsets