docs: def on_toggle_sticky_clicked(self, event, state_m):
          """Callback for the "toggle-sticky-check-button" emitted by custom TabLabel widget.
          """
          [page, state_identifier] = self.find_page_of_state_m(state_m)
          if not page:
              return
          self.tabs[state_identifier]['is_sticky'] = not self.tabs[state_identifier]['is_sticky']
          page.sticky_button.set_active(self.tabs[state_identifier]['is_sticky'])