Sounds good.

I'd be interested in chatting more (maybe next week by voice).  Curious if you ever push/pop more than one item in responds to enter, content, or exit.  If always one (or zero), it seems like this could be handled by arguments passed to and returns from `onEnter` and `onExit` methods.  I'm not yet seeing the need for `onContent`, but I'm probably imagining something different.

And as below, the hash/registry of parsers needs to be keyed by namespace URI and local name (e.g. `{http://www.opengis.net/kml/2.2}Placemark`).  So we can properly handle Atom in our KML, GeoRSS in our Atom, GeoRSS and GML in our RSS, etc.