code: def focusNextPrevChild(self, next_child):
          
          fd = focus_registry.focused_declaration()
          if next_child:
              child = self.declaration.next_focus_child(fd)
              reason = Qt.TabFocusReason
          else:
              child = self.declaration.previous_focus_child(fd)
              reason = Qt.BacktabFocusReason
          if child is not None and child.proxy_is_active:
              return child.proxy.tab_focus_request(reason)
          widget = self.widget
          return type(widget).focusNextPrevChild(widget, next_child)
docs: The default 'focusNextPrevChild' implementation.