[gtk+] doc: Document the GDK_BACKEND environment variable

[Benjamin Otte <otte src gnome org>]

commit 9f5c734e146baac0d21dfacf2b757f8dfaf6aed9
Author: Benjamin Otte <otte redhat com>
Date:   Sat Feb 12 22:03:08 2011 +0100

    doc: Document the GDK_BACKEND environment variable

 docs/reference/gtk/running.sgml |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/gtk/running.sgml b/docs/reference/gtk/running.sgml
index 40a70d7..74a0a37 100644
--- a/docs/reference/gtk/running.sgml
+++ b/docs/reference/gtk/running.sgml
@@ -392,6 +392,34 @@ nevertheless.
 </formalpara>
 
 <formalpara>
+  <title><envar>GDK_BACKEND</envar></title>
+
+  <para>
+    If set, selects the GDK backend to use. Selecting a backend requires that GTK is compiled
+    with support for that backend. The following backends can be selected:
+    <variablelist>
+
+      <varlistentry>
+        <term>quartz</term>
+        <listitem><para>Selects the native Quartz backend</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>win32</term>
+        <listitem><para>Selects the native backend for Microsoft Windows</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>x11</term>
+        <listitem><para>Selects the native backend for connecting to X11 servers.</para></listitem>
+      </varlistentry>
+
+    </variablelist>
+    For more information about selecting backends, see the gdk_display_manager_get() function.
+  </para>
+</formalpara>
+
+<formalpara>
   <title><envar>GDK_SYNCHRONIZE</envar></title>
 
   <para>