Peter Hosey has released LMX, an event
based reverse XML parser for Objective C on Mac OS X. It starts at the end of the document and parses forward, rather than the other way around. "It has mostly the same API as NSXMLParser; if you're used to NSXMLParser, LMX should have no learning curve for you (other than the mind-bendingness of events coming in in the reverse order)." LMX is published under a BSD license.
