Validating XML

Hello,

I am examining options for validating XML documents either using XSD 
schema or something like schematron (DTD are not robust enough for my 
needs), and am wondering what other PHP developers are using to do this.

  I saw that the new simpleXML extension did have a method that appeared 
to validate XML against a schema file, but this method now appears to be 
removed from the current PHP 5 release candidate.  What other options 
are available to PHP?  I have come across a schematron class on 
sourceforge (http://phpxmlclasses.sourceforge.net/), but am not to sure 
how good it is.  Also, Krysalis (http://www.interakt.ro/) does appear to 
include some functionality that attempts to validate XML against a 
schema, but, again, it is unclear how good this implementation is.

Anyway, I'm eager to hear other's suggestions and experiences.

Michael