public Parser xmlSchemaIs() {
        if (xmlSchemaIsParser == null) {
           FutureParser future = scoped("xmlSchemaIs");
           xmlSchemaIsParser = future;
           future.setParser(
               sequence(
                   token("XML-SCHEMA"),
                   identifier(),
                   optional(
                       token("IS")
                   ),
                   choice(
                       dataName(),
                       literal()
                   )
               )
           );
        }

        return xmlSchemaIsParser;
    }