valid [validation-scheme] [id]
Check and report the validity of the document id with respect to a DTD, RelaxNG, or XSD schemas specified in validation-scheme (see validate for information, on how validation-scheme may be specified). Prints "yes" if the document is valid and "no" otherwise. If no document identifier is given, the current document is used. If no validation-scheme is specified, the validity against the DTD subset is checked.