However, parsing the RNC files fails because of the Datatype Library with the "http://whattf.org/datatype-draft" namespace:
datatype library "http://whattf.org/datatype-draft" not recognized | html5/web-forms.rnc
Validator.nu provides a Pluggable Datatype Library for that namespace (available here). I've copied it in the ${oxygenHome}/lib/ directory and even added it to the XHTML5 classpath in the Document Type Association preferences.
However, it doesn't solve the issue. I don't know if it's a problem with the .jar, the service for org.relaxng.datatype.DatatypeLibraryFactory and I don't know what to do to make it works.





data server software 