set_default() sets the child widget passed to it as the default child. (This will usually be a GtkButton.) The child must have the flag GTK_CAN_DEFAULT set in order to be allowed focus. Some widgets are created with this flag already set; GtkButton is not one of those widgets, and needs to be flagged.

Child widgets that are set as default are marked as such in a way that will be familiar to users. For instance, a button set as default has a decorative frame and shadow around it.

See also: GtkWidgetFlags, GtkWidget, set_flags() .