Sax vs DOM parser: please explain this difference

This is probably a general-knowledge parser question… Can someone explain why the SAX parser does not see the SOAP:Envelope element when I submit a request to my agent and run the documentcontext through the saxparser? The SAX parser sees only as far as the Request_content element and its child text element.

What I’m doing is as follows:

  1. Submit a SOAP:Envelope to a Lotusscript agent

  2. From the agent, run the notessession.documentcontext through the saxparser

  3. Step through the Request_content item (which contains the SOAP envelope) to locate the method to invoke.

Step 3 works fine if I use the DOM parser to locate the method. But when I use the saxparser, it doesn’t any elements under the Request_Content’s text element. If I print out all the elementnames the saxparser sees, the list goes no deeper than item/text:

“document, noteinfo, created, datetime, modified, datetime, revised, datetime, lastaccessed, datetime, addedtofile, datetime, item, text, item, text, item, text, item, text…” (Note: no SOAP:Envelope)

Why the difference?