The USE_XFCE variable is used to autoconfigure the dependencies for ports which use an Xfce based library or application like x11-toolkits/libxfce4gui and x11-wm/xfce4-panel.
The following Xfce libraries and applications are recognized at the moment:
libexo: x11/libexo
libgui: x11-toolkits/libxfce4gui
libutil: x11/libxfce4util
libmcs: x11/libxfce4mcs
mcsmanager: sysutils/xfce4-mcs-manager
panel: x11-wm/xfce4-panel
thunar: x11-fm/thunar
wm: x11-wm/xfce4-wm
xfdev: dev/xfce4-dev-tools
The following additional parameters are recognized:
configenv: Use this if your port requires a special modified CONFIGURE_ENV to find its required libraries.
-I${LOCALBASE}/include -L${LOCALBASE}/lib
gets added to CPPFLAGS to CONFIGURE_ENV.
Therefore, if a port has a dependency on sysutils/xfce4-mcs-manager and requires the special CPPFLAGS in its configure environment, the syntax will be:
USE_XFCE= mcsmanager configenv