code: def indent(self, value):
          
          # Explicit indent setting
          if isinstance(value, str):
              if value.isspace() or len(value) == 0:
                  self._indent = value
              else:
                  raise ValueError('String indentation can only contain '
                                   'whitespace.')
  
          # Set indent width
          elif isinstance(value, int):
              if value >= 0:
                  self._indent = value * ' '
              else:
                  raise ValueError('Indentation spacing must be nonnegative.')
  
          else:
              raise TypeError('Indentation must be specified by string or space '
                              'width.')
docs: Validate and set the indent width.