Schematron rules can be embedded into W3C Schema through annotation (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).
<?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"?>