 
GML Combo Box Widget
Defines a GUI combo box widget. Another name for this would be a dropdown or select.
@GUI::ComboBox
@GUI::ComboBox {
    name: "msgbox_icon_combobox"
    model_only: true
}
@GUI::ComboBox {
    name: "msgbox_buttons_combobox"
    model_only: true
}| Property | Type | Possible values | Description | 
|---|---|---|---|
| placeholder | string | Any string | Editor placeholder | 
| model_only | bool | true or false | Only allow values from model |