Greg Beaver - Update to libxml2 in PHP - progress hath been acquired:

"I am abandoning the creation of a relax NG schema in favor of the battle-tested xsd. The error messages for xsd validation are far clearer than the rng ones."

W3C Schema/Relax NG/DTD seem to be totally useless in PHP, help?:

"Now that I am working on the PHP 5+ implementation of Pyrus, the first thing I thought I might do is create a Relax NG schema that the PHP libxml can handle. After an entire day of fighting with the thing, I've managed to discover more than 10 simple and valid Relax NG schema that simply don't work with the version of libxml distributed with PHP 5.2.3. In addition, with helpful error messages like "Expecting name, got nothing here," even with the use of libxml_use_internal_errors() I find the error reporting to be excruciatingly useless."