Schematron rules can be embedded into an XML Schema through annotations (using the appinfo element), or in any element on any level of a RELAX NG Schema (taking into account that the RELAX NG validator ignores all elements that are not in the RELAX NG namespace).
Oxygen XML Editor accepts such documents as Schematron validation schemas and it is able to extract and use the embedded rules. To validate an XML document with both RELAX NG schema and its embedded Schematron rules, you need to associate the document with both schemas. For example:
<?xml-model href="percent.rng" type="application/xml" schematypens="http://relaxng.org/ns/structure/1.0"?> <?xml-model href="percent.rng" type="application/xml" schematypens="http://purl.oclc.org/dsdl/schematron"?>
<?xml-model href="percent.xsd" type="application/xml" schematypens="http://purl.oclc.org/dsdl/schematron"?>