* or just <firstterm>UI definitions</firstterm> if the context is clear. Do not
* confuse GtkBuilder UI Definitions with
* <link linkend="XML-UI">GtkUIManager UI Definitions</link>, which are more
- * limited in scope.
+ * limited in scope. It is common to use <filename>.ui</filename> as the filename extension for files containing GtkBuilder UI definitions.
* </para>
* <programlisting>
* <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" parse="text" href="../../../../gtk/gtkbuilder.rnc">