Undocumented in source.
A GtkComboBox is a widget that allows the user to choose from a list of valid choices. The GtkComboBox displays the selected choice. When activated, the GtkComboBox displays a popup which allows the user to make a new choice. The style in which the selected value is displayed, and the style of the popup is determined by the current theme. It may be similar to a Windows-style combo box.