Right now (with bug 1369584 fixed) we just put all selectors with an id in the revalidation selector list. We can do better. As https://github.com/servo/servo/pull/17055#issuecomment-304436932 points out, it's enough to insert the ones which contain an id which is not present in the relevant rulehash (selectormap). I'm deferring this for now in the interests of getting bug 1369584 landed, but we should really do it. Though it might make sense to wait until after bug 1362538.