code: def istring(self, in_string=''):
          
          new_string = IString(in_string)
          new_string.set_std(self.features.get('casemapping'))
          if not self._casemap_set:
              self._imaps.append(new_string)
          return new_string
docs: Return a string that uses this server's IRC casemapping.
  
          This string's equality with other strings, ``lower()``, and ``upper()`` takes this
          server's casemapping into account. This should be used for things such as nicks and
          channel names, where comparing strings using the correct casemapping can be very
          important.