Several XML vocabularies have been specified in Relax NG. You may want to take a look at the following:
There is an online service at http://validator.nu for validating XML documents against schemas written in Relax NG. To use it, however, you must put the Relax NG Schema document on the web so that it is accessible by a URL. You can use the following two links (which I have prepared from examples in the RELAX NG Tutorial) to test this online validator:
Note: You may want to set the following switches:
Encoding: As set by the server/page Preset: None Parser: XML: don't load external entities
and check the following box:
Be lax about HTTP Content-Type