An SAX parser is the base technology for all of the standard library DOM and JAXB functions - I'm not sure what StaX uses.
If you are curious about the details why not download the standard
Java library source code? It is very instructive to browse in.
For example I just searched for Stax in the Java 6 source and found lots of org.apache.xalan. and org.apache.xerces references.
Bill