Document 'use-default-font-for-symbols' more

"why does my set-fontset-font call not work for symbols" is a common
question, and it's because 'use-default-font-for-symbols' is not
discoverable enough.

* doc/emacs/mule.texi (Modifying Fontsets): Mention it here.
* doc/lispref/display.texi (Fontsets): And here.
* src/fontset.c (Fset_fontset_font): And most importantly here.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/fontset.c b/src/fontset.c
index a98d75606b3..bac04119957 100644
--- a/src/fontset.c
+++ b/src/fontset.c
@@ -1501,7 +1501,8 @@ CHARACTERS may be a script symbol.  In that case, use FONT-SPEC for
 all the characters that belong to the script.  See the variable
 `script-representative-chars' for the list of known scripts, and
 see the variable `char-script-table' for the script of any specific
-character.
+character.  Note: for the `symbol' script only, whether the FONTSET
+is actually used depends on the value of `use-default-font-for-symbols'.
 
 CHARACTERS may be a charset symbol.  In that case, use FONT-SPEC for
 all the characters in the charset.  See `list-character-sets' and