[webkit-dev] How to determine the " could cut " status ?

Hi, all, When I select a whole page, I could copy and paste it to other place. But most of the time I select a page, I'm not allowed to cut it since the browser does not permit it. So how could I query the status to determine whether I could copy or cut ? Is there any API method I could use ? Or I should judge it by myself ? Anybody could give a hint ? Thanks so much. Best Regards. Andy