def validate(self, val):
self.validate_type_only(val)<EOL>if not hasattr(val, '<STR_LIT>') or val._tag is None:<EOL><INDENT>raise ValidationError('<STR_LIT>')<EOL><DEDENT>return val<EOL>
For a val to pass validation, it must have a _tag set. This assumes
that the object validated that _tag is a valid tag, and that any
associated value has also been validated.