optional_depends tk "" "" "for Tk support" &&
optional_depends gtk+2 \
                 "--enable-gtk=yes" \
                 "--enable-gtk=no" \
                 "for GTK+ GUI support"
if is_depends_enabled $SPELL gtk+2 ; then
    config_query GTK_BLOX "Build EXPERIMENTAL GTK+ version of BLOX?" n &&
    if [[ "$GTK_BLOX" = "y" ]]; then 
      depends gtk+2 "--enable-gtk=blox"
    fi
fi

.