There's no markup or API for dialog boxes, tool palettes, hovering tooltips, the contents of popup widgets, and the like.
Real world examples today
* http://www.reddit.com/ - make sure to be logged out if you have an account, and click the register link * http://reddit.com/ - make sure to be logged out if you have an account, and click the Join Digg! button
- The tooltips in the table of  are interesting because they are currently <div>s and force the parent to be a TD rather than a TH since TH is inline only, even though the visible content is really just phrasing content.