要在扩展中添加悬停框，您必须将值传递给[widgetInstance].title.caption例如：

const extension: JupyterFrontEndPlugin<void> = {
  id: 'some-id',
  autoStart: true || false,
  activate: async(app: JupyterFrontEnd, palette: ICommandPalette) => {
     const { commands } = app;
      let widget1: widget= new widget(); // create the widget
      widget1.id = 'widget1-id';
      widget1.title.label = 'widget Label';
      widget1.title.caption="widget hovering text description"; // this will show the text when you hover over an extension
      app.shell.add(widget1, 'right', { rank: 1 });
      ...
      ...
      ... rest of your code ...

}