resource:  XML Specification: http://www.w3.org/TR/2000/REC-xml-20001006   XML resource http://www.w3.org/XML/     RELAX NG Another popular schema language for XML is RELAX NG . Initially specified by OASIS , RELAX NG is now also an ISO international standard (as part of DSDL ). It has two formats: an XML based syntax and a