def get_selected_tab(self):
        """Returns the tab specific by the GET request parameter.

        In the event that there is no GET request parameter, the value
        of the query parameter is invalid, or the tab is not allowed/enabled,
        the return value of this function is None.
        """
        selected = self.request.GET.get(self.param_name, None)
        if selected:
            try:
                tab_group, tab_name = selected.split(SEPARATOR)
            except ValueError:
                return None
            if tab_group == self.get_id():
                self._selected = self.get_tab(tab_name)
        return self._selected
Returns the tab specific by the GET request parameter.

        In the event that there is no GET request parameter, the value
        of the query parameter is invalid, or the tab is not allowed/enabled,
        the return value of this function is None.