set-face-font doc string update

* lisp/faces.el (set-face-font): Mention what the string formats
are (bug#14647).

diff --git a/lisp/faces.el b/lisp/faces.el
index 2779197804b88e5bdbf647eeb8311832d19fbe48..75753ecefc931c966fd7f2829c93d2f568db1630 100644 (file)
--- a/lisp/faces.el
+++ b/lisp/faces.el
@@ -888,6 +888,10 @@ Use `set-face-attribute' for finer control of font weight and slant."
 
 (defun set-face-font (face font &optional frame)
   "Change font-related attributes of FACE to those of FONT (a string).
+The format of the font varies based on the font system in used,
+but it can commonly be an X logical font description (XLFD)
+string, or a simpler XFD string like \"courier:size=10\".
+
 FRAME nil or not specified means change face on all frames.
 This sets the attributes `:family', `:foundry', `:width',
 `:height', `:weight', and `:slant'.  When called interactively,