code: def _check_value(self, tag, value):
          
          if value is None:
              if self._schema.children_min_occurs[tag] > 0:
                  raise WSDLParseError("Missing tag '%s'" % tag)
              return value
          return value
docs: Ensure that the element matching C{tag} can have the given C{value}.
  
          @param tag: The tag to consider.
          @param value: The value to check
          @return: The unchanged L{value}, if valid.
          @raises L{WSDLParseError}: If the value is invalid.