Describe how to debug fontconfig issues

* etc/PROBLEMS: Add FC_DEBUG usage pointers.

diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index f396dc3a0001584c9f180121c7a8970384c7731f..2d3bc0c94017e790fd81bfefd79218214c1fb7b9 100644 (file)
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -751,6 +751,18 @@ Try removing or moving aside "$XDG_CONFIG_HOME/fontconfig/conf.d" and
 "$XDG_CONFIG_HOME/fontconfig/fonts.conf"
 ($XDG_CONFIG_HOME is treated as "~/.config" if not set)
 
+Running Emacs as
+
+    FC_DEBUG=1024 emacs
+
+will cause fontconfig to output information about which configuration
+files it is reading.  Running Emacs as
+
+    FC_DEBUG=1 emacs
+
+will result in information about the results of fontconfig's font
+matching (including the filename(s) of the resulting fonts).
+
 *** This can occur when two different versions of FontConfig are used.
 For example, XFree86 4.3.0 has one version and Gnome usually comes
 with a newer version.  Emacs compiled with Gtk+ will then use the