Operations on pull requests in merge queue #2943

Is there a method to check if a pull request is in merge queue? There is an is_merged() method but it doesn't help tell if a pull request is in the queue open or just open. I've also noticed for a merging pull request the mergeable_state is unstable, is it something we are supposed to use? What does unstable mean?

Also is there a method to jump queue so that a pull request can be moved to the head position?