__init__ (
        self,
        master,
        widget_dict,
        start=None,
        **config,
        )

init frame, containing:

• tabbs

• frame with fixed width, height for switched widgets

size from slaves is not propagated

change_tab ( self,  key )

process of changing:

• lifts actual tab

• changes color of previous tab to background

• actual tab is marked white

• releases (forget) previous widget

• pack actual widget

tab_selected ( self,  event )

event handler for tabs