InfoPath Dev

I'm researching it because I wanted to verify that I was using the same XML validation engine in the program I'm using to write my XML schemas...Stylus Studio XML Pro.

Thanks for the 'Welcomes' & responses. OK I got it down to the MSXML thing...now I'm wondering if there's a certain version of MSXML that is used by default....for example MSXML 4.0 DOM Parser, or MSXML 4.0 SAX Parser, or something else. Any thoughts?

Does anyone know what the default validation engine is that InfoPath uses to validate a document?