diff --git a/data/zenity.1 b/data/zenity.1
index 9acfcc4..63e5a15 100644
--- a/data/zenity.1
+++ b/data/zenity.1
@@ -282,6 +282,12 @@ Show version of program.
 .PP
 Also the standard GTK+ options are accepted.
 
+.SH ENVIRONMENT
+
+Normally, zenity detects the terminal window from which it was launched and
+keeps itself above that window.  This behavior can be disabled by unsetting the
+WINDOWID environment variable.
+
 .SH EXAMPLES
 
 Display a file selector with the title \fISelect a file to
diff --git a/help/C/zenity.xml b/help/C/zenity.xml
index 0730e8f..393585b 100644
--- a/help/C/zenity.xml
+++ b/help/C/zenity.xml
@@ -460,6 +460,19 @@
 
   </sect2>
 
+<!-- ==== Environment variables ==== -->
+
+  <sect2 id="zenity-environment-variables">
+    <title>Environment Variables</title>
+
+    <para>
+      Normally, &app; detects the terminal window from which it was launched
+      and keeps itself above that window.  This behavior can be disabled by
+      unsetting the <envar>WINDOWID</envar> environment variable.
+    </para>
+
+  </sect2>
+
   </sect1>
 <!-- ==== Calendar Options ====== -->