The mode of the size group determines the directions in which the size group affects the requested sizes of its component widgets.

(define-g-enum "GtkSizeGroupMode" gtk-size-group-mode
  (:export t
   :type-initializer "gtk_size_group_mode_get_type")
  (:none 0)
  (:horizontal 1)
  (:vertical 2)
  (:both 3))  

:none

Group has no effect.

:horizontal

Group affects horizontal requisition.

:vertical

Group affects vertical requisition.

:both

Group affects both horizontal and vertical requisition.