* GTK+ (http://www.gtk.org/), version 3.22.0 or later.
* GtkSourceView (http://projects.gnome.org/gtksourceview/)
- version 3.4.0 or later.
+ version 3.x (3.4.2 or later) or 4.x.
* GNU Spread Sheet Widget (http://www.gnu.org/software/ssw)
version 0.7 or later.