docs: def set_std(self, std):
          """Set the standard we'll be using (isupport CASEMAPPING)."""
          if not hasattr(self, '_std'):
              IMap.__init__(self)
  
          # translation based on std
          self._std = std.lower()
  
          # set casemapping maps
          self._set_transmaps()
  
          # create translations
          if self._lower_chars:
              self._lower_trans = str.maketrans(self._upper_chars, self._lower_chars)
          if self._upper_chars:
              self._upper_trans = str.maketrans(self._lower_chars, self._upper_chars)