'Returns a list of the default classes for the tab.
Defaults to and empty list (``[]``), however additional classes may
be added depending on the state of the tab as follows:
If the tab is the active tab for the tab group, in which
the class ``"active"`` will be added.
If the tab is not enabled, the classes the class ``"disabled"``
will be added.'

def get_default_classes(self):

    default_classes = super(Tab, self).get_default_classes()
    if self.is_active():
        default_classes.extend(CSS_ACTIVE_TAB_CLASSES)
    if (not self._enabled):
        default_classes.extend(CSS_DISABLED_TAB_CLASSES)
    return default_classes
