|GTK+ Reference Manual|
Sometimes it is preferable to display the available options not in a linear list, but in a grid. A typical example would be a "color combo" where the individual items are small square color swatches. The new widgets support gridded display with the functions gtk_combo_box_set_wrap_width(), gtk_combo_box_set_row_span_column() and gtk_combo_box_set_column_span_column().
|Display of icons||
An often-heard complaint about GtkOptionMenu is that the icons which appear in the image menu items in its menu are not displayed in the button showing the selected item. This limitation has been removed in GtkComboBox; the selected item appears in the same way as the options in the popup.
|Full tree model power||
Since the new widgets are built around the same models that are used for GtkTreeView, all of the powerful machinery of tree models and cell renderers can be used.