void register_widget_control ( string name, callback [, int width [, int height ] ] )
Adds the output of callback to the admin interface as an inline popup. The popup is a child of the main form so it must not include <form> tags or submit buttons. It should include form inputs with very specific names and id’s.
The form data should also be handled within callback as its first action, but advanced widgets may have good reasons to differ from this model.
The string name used in register_widget_control() needs to match the string name used in register_sidebar_widget().
Widgets: is_active_widget(), the_widget(), register_widget(), unregister_widget(), wp_register_widget_control(), wp_unregister_widget_control(), wp_convert_widget_settings(), wp_get_widget_defaults(), wp_widget_description()