Allow xdg-settings to set the default OS handler for url protocols.

scripts/desc/xdg-settings.xml

 <?xml version="1.0"?>
 <?xml-stylesheet type="text/xsl"
    href="http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl"?>
 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
     "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [
 ]>
 <refentry id="xdg-settings">
   <refentryinfo>
     <title>xdg-settings Manual</title>
     <copyright>
-      <year>2009</year>
+      <year>2009-2011</year>
     </copyright>
     <author>
       <firstname>Mike</firstname>
       <surname>Mammarella</surname>
     </author>
     <address><email>mdm@google.com</email></address>
     <!--<releaseinfo>xdg-utils 1.0</releaseinfo>-->
   </refentryinfo>
 
   <refmeta>
@@ skipping 11 matching lines @@
       <command>xdg-settings</command>
       <group choice="req">
         <arg choice="plain"><option><replaceable>get</replaceable></option></arg>
         <arg choice="plain"><option><replaceable>check</replaceable></option></arg>
         <arg choice="plain"><option><replaceable>set</replaceable></option></arg>
       </group>
       <group choice="req">
         <option>property</option>
       </group>
       <group choice="opt">
+        <option>subproperty</option>
+      </group>
+      <group choice="opt">
         <option>value</option>
       </group>
     </cmdsynopsis>
     <cmdsynopsis>
       <command>xdg-settings</command>
       <group choice="req">
         <arg choice="plain"><option>--help</option></arg>
         <arg choice="plain"><option>--list</option></arg>
         <arg choice="plain"><option>--manual</option></arg>
         <arg choice="plain"><option>--version</option></arg>
@@ skipping 48 matching lines @@
       <varlistentry>
         <term><option>--version</option></term>
         <listitem>
           <simpara>
             Show the xdg-utils version information.
           </simpara>
         </listitem>
       </varlistentry>
     </variablelist>
   </refsect1>
+  <refsect1 id="properties">
+    <title>Properties</title>
+    <para>
+      When using xdg-settings to get, check or set a destkop setting, properties
+      and possibly sub-properties are used to specify the setting to be changed.
+    </para>
+    <para>
+      Some properties (such as default-web-browser) fully describe the setting
+      to be changed. Other properties (such as default-url-scheme-handler) require
+      more information (in this case the actual scheme to set the default handler
+      for) which must be provided in a sub-property.
+    </para>
+  </refsect1>
   <refsect1 id="exitcodes">
     <title>Exit Codes</title>
     <para>
       An exit code of 0 indicates success while a non-zero exit code
       indicates failure. The following failure codes can be returned:
     </para>
     <variablelist>
       <varlistentry>
         <term><option>1</option></term>
         <listitem>
@@ skipping 43 matching lines @@
       <programlisting>
         xdg-settings check default-web-browser firefox.desktop
       </programlisting>
     </para>
     <para>
       Set the default web browser to google-chrome.desktop
       <programlisting>
         xdg-settings set default-web-browser google-chrome.desktop
       </programlisting>
     </para>
+    <para>
+      Set the default mailto URL scheme handler to be evolution.desktop
+      <programlisting>
+        xdg-settings set default-url-scheme-handler mailto evolution.desktop
+      </programlisting>
+    </para>
   </refsect1>
 </refentry>