Sets whether tool_item should be considered important. The GtkToolButton
class uses this property to determine whether to show or hide its label
when the toolbar style is GTK_TOOLBAR_BOTH_HORIZ. The result is that
only tool buttons with the "is_important" property set have labels, an
effect known as "priority text"
Since 2.4
Sets whether tool_item should be considered important. The GtkToolButton class uses this property to determine whether to show or hide its label when the toolbar style is GTK_TOOLBAR_BOTH_HORIZ. The result is that only tool buttons with the "is_important" property set have labels, an effect known as "priority text" Since 2.4