Doing QA on an XML parser

I've been faced with the task of doing quality assurance of a developing XML 
parser. This turns me pale, because I know of few tasks that are more 
difficult or crucial.

The goal is more specifically a non-validating XML parser that conforms to XML 
1.0 and XML Namespaces 1.0.

How does one achieve that task?

What I find the tricky part of this, is knowing when one have done it 
correctly, and in fact have done it at all, and haven't missed anything. What 
is the correct regression testing/quality assurance to perform on an XML 
parser? How does one avoid ending up with junk?

For instance, if one pass W3C's XML Test Suite[1], does that mean anything in 
practice, or must one resort to some other kind of conformance testing in 
addition? What do others do?

Generally, any advice or sharing of hard-earned experiences are of interest.


Thanks in advance,

		Frans

1.
http://www.w3.org/XML/Test/