Document syntax-ppss-context

* doc/lispref/syntax.texi (Parser State): Document it.

* lisp/emacs-lisp/syntax.el (syntax-ppss-context): Add a doc
string (bug#32504).

doc/lispref/syntax.texi

@@ -882,6 +882,11 @@ The value is @code{nil} if @var{state} represents a parse which has
 arrived at a top level position.
 @end defun
 
+@defun syntax-ppss-context state
+Return @code{string} if @var{state} is a string and @code{comment} if
+it's a comment.
+@end defun
+
 @node Low-Level Parsing
 @subsection Low-Level Parsing
 

lisp/emacs-lisp/syntax.el

@@ -371,6 +371,10 @@ itself at the outermost level), return nil."
       (nth 8 ppss)))
 
 (defsubst syntax-ppss-context (ppss)
+  "Say whether PPSS is a string, a comment, or something else.
+If PPSS is a string, the symbol `string' is returned.  If it's a
+comment, the symbol `comment' is returned.  If it's something
+else, nil is returned."
   (cond
    ((nth 3 ppss) 'string)
    ((nth 4 ppss) 'comment)