(facep): Doc fix.

lisp/faces.el

@@ -204,7 +204,10 @@ If NAME is already a face, it is simply returned."
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (defun facep (face)
-  "Return non-nil if FACE is a face name."
+  "Return non-nil if FACE is a face name or internal face object.
+Return nil otherwise.  A face name can be a string or a symbol.
+An internal face object is a vector of the kind used internally
+to record face data."
   (internal-lisp-face-p face))