<sect1>

      <title>Optional dependencies</title>

      <para>Some large applications can be built in a number of

	configurations, adding functionality if one of a number of

	libraries or applications is available. Since not all users

	want those libraries or applications, the ports system

	provides hooks that the port author can use to decide which

	configuration should be built. Supporting these properly will

	make uses happy, and effectively provide 2 or more ports for the

	price of one.</para>

      <para>The easiest of these to use is

	<literal>WITHOUT_X</literal>. If the port can be built both

	with and without X support, then it should normally be built

	with X support. If <literal>WITHOUT_X</literal> is defined,

	then the version that does not have X support should be

	built.</para>

      <para>Various parts of GNOME have such knobs, though they are

	slightly more difficult to use. The variables to use in the

	<filename>Makefile</filename> are <makevar>WANT_*</makevar>

	and <makevar>HAVE_*</makevar>. If the application can be

	built both with or without one of the dependencies listed

	below, then the <filename>Makefile</filename> should set

	<makevar>WANT_PKG</makevar>, and should build the version that

	uses <makevar>PKG</makevar> if <makevar>HAVE_PKG</makevar>

	is defined.</para>

      <para>The <makevar>WANT_*</makevar> variables currently

	supported this way are <makevar>WANT_GLIB</makevar>,

	<makevar>WANT_GTK</makevar>, <makevar>WANT_ESOUND</makevar>,

	<makevar>WANT_IMLIB</makevar>, and

	<makevar>WANT_GNOME</makevar>.</para>

      </sect1>