; Review and fix NEWS and related documentation

* etc/NEWS: Fix wording, punctuation, and markup.

* lisp/emacs-lisp/subr-x.el (string-glyph-split): Doc fix.

* doc/lispref/display.texi (Displaying Messages): Document
'set-message-functions'.

doc/lispref/display.texi

@@ -346,6 +346,20 @@ The default value is the function that clears the message displayed in
 an active minibuffer.
 @end defvar
 
+@defopt set-message-functions
+The value of this user option is a list of functions to be called for
+handling display of echo-area messages.  Each function is called with
+one argument, the text of the message to display.  If the function
+returns a string, that string replaces the original message, and the
+next function in the list is called with the new message text.  If the
+function returns @code{nil}, the next function in the list is called
+with the same text; if the last function in the list returns
+@code{nil}, the message text is displayed in the echo area.  If the
+function returns a non-@code{nil} value that is not a string, the
+message is considered to be handled, and no further functions in the
+list are called.
+@end defopt
+
 @defvar inhibit-message
 When this variable is non-@code{nil}, @code{message} and related functions
 will not use the Echo Area to display messages.

lisp/emacs-lisp/subr-x.el

@@ -333,7 +333,10 @@ as the new values of the bound variables in the recursive invocation."
 ;;;###autoload
 (defun string-glyph-split (string)
   "Split STRING into a list of strings representing separate glyphs.
-This takes into account combining characters and grapheme clusters."
+This takes into account combining characters and grapheme clusters:
+if compositions are enbaled, each sequence of characters composed
+on display into a single grapheme cluster is treated as a single
+indivisible unit."
   (let ((result nil)
         (start 0)
         comp)