code: def set_qualifier(self, value):
          
          if self.allows_qualifier:
              self.qualifier = value.strip()
          else:
              raise UNTLStructureException(
                  'Element "%s" does not allow a qualifier' % (self.tag,)
              )
docs: Set the qualifier for the element.
  
          Verifies the element is allowed to have a qualifier, and
          throws an exception if not.