For the next stable release (4.12) I would like to replace Mk/bsd.xfce.mk file by Mk/Uses/xfce.mk.
In Xfce repository trunk branch already uses it.
Now, dependencies are well detected.
Usage is USES= xfce or USES= xfce:gtk3
gtk3 is necessary because some applications (Mousepad, xfce4-appfinder, xfce4-panel) support Gtk3 (optional), whereas it's mandatory in Parole. We need to test, if Gtk3 has been enabled in x11/libxfce4menu.
I also added warning message, when port uses libgui (x11-toolkits/libxfce4gui) because this library is not anymore maintained by upstream, and requires patch due changes in x11/libxfce4util.