code: def schemes(self):
          
          if not self._schemes:
              _schemes = []
              if self.types.keys() & _HTTP_PROTOS:
                  _schemes.append('HTTP')
              if self.types.keys() & _HTTPS_PROTOS:
                  _schemes.append('HTTPS')
              self._schemes = tuple(_schemes)
          return self._schemes
docs: Return supported schemes.