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, 3 insertions, 1 deletions

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 011738df268..a9f89406070 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -3983,7 +3983,9 @@ that case, use @var{font-spec} for all the characters in the charset.
 
 @var{characters} may be a script symbol (@pxref{Character Properties,
 char-script-table}).  In that case, use @var{font-spec} for all the
-characters belonging to the script.
+characters belonging to the script.  See also
+@code{use-default-font-for-symbols}, which affects font selection
+when @var{fontset} is @code{symbol}.
 
 @var{characters} may be @code{nil}, which means to use @var{font-spec}
 for any character in @var{fontset} for which no font-spec is