Return a unicode object with the MATCH representation of this GlobalContextField.

def to_match(self):
        """Return a unicode object with the MATCH representation of this GlobalContextField."""
        self.validate()

        mark_name, field_name = self.location.get_location_name()
        validate_safe_string(mark_name)
        validate_safe_string(field_name)

        return u'%s.%s' % (mark_name, field_name)