Minor detail/question:
Would it be possible to make the layout of the 'Properties' frame as compact with regard to vertical spacing as 'General' and 'Object Types'?
(I didn't find anything obvious in the widget tree which sets the vertical spacing between the two GtkHBoxes - obviously the other two option frames use two GtkVboxes in a GtkHBox, and the GtkCheckButtons inside those GtkVBox containers are more tightly arranged with regard to vertical spacing than two GtkHBoxes in a GtkVBox)
Minor detail/question:
Would it be possible to make the layout of the 'Properties' frame as compact with regard to vertical spacing as 'General' and 'Object Types'?
(I didn't find anything obvious in the widget tree which sets the vertical spacing between the two GtkHBoxes - obviously the other two option frames use two GtkVboxes in a GtkHBox, and the GtkCheckButtons inside those GtkVBox containers are more tightly arranged with regard to vertical spacing than two GtkHBoxes in a GtkVBox)