Add doc for description element and update fonts.dtd

Fixes https://gitlab.freedesktop.org/fontconfig/fontconfig/issues/133

doc/fontconfig-user.sgml

@@ -339,6 +339,11 @@ the library.  If 'prefix' is set to "xdg", the value in the XDG_CONFIG_HOME envi
 This element provides a place to consolidate additional configuration
 information.  <literal>&lt;config&gt;</literal> can contain <literal>&lt;blank&gt;</literal> and <literal>&lt;rescan&gt;</literal> elements in any
 order.
+  </para></refsect2>
+  <refsect2><title><literal>&lt;description domain="fontconfig-conf"&gt;</literal></title><para>
+This element is supposed to hold strings which describe what a config is used for.
+This string can be translated through gettext. 'domain' needs to be set the proper name to apply then.
+fontconfig will tries to retrieve translations with 'domain' from gettext.
   </para></refsect2>
   <refsect2><title><literal>&lt;blank&gt;</literal></title><para>
 Fonts often include "broken" glyphs which appear in the encoding but are

fonts.dtd

@@ -1,12 +1,13 @@
 <!-- This is the Document Type Definition for font configuration files -->
-<!ELEMENT fontconfig (dir | 
+<!ELEMENT fontconfig (alias |
 		      cache | 
 		      cachedir |
-		      include | 
 		      config |
-		      selectfont |
+		      description |
+		      dir |
+		      include |
 		      match |
-		      alias)* >
+		      selectfont)* >
 
 <!-- 
     Add a directory that provides fonts
@@ -43,6 +44,16 @@
 	  prefix    CDATA      "default"
 	  xml:space (default|preserve) 'preserve'>
 
+<!--
+    Set a string as a description for the targeted config file
+
+    Set 'domain' to change where to pull translations from.
+    This will be done through gettext.
+-->
+<!ELEMENT description (#PCDATA)>
+<!ATTLIST description
+	  domain	CDATA	"fontconfig-conf">
+
 <!--
     Reference another configuration file; note that this
     is another complete font configuration file and not