MarsSeed [1] filed a deletion request for libxfcegui4 [2]: EOL Gtk2 based lib from 2012; not compatible with current Gtk3 based Xfce4.
No longer useful to keep. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/libxfcegui4/
