docs: def indent(indent_str=None):
      """
      An example indentation ruleset.
      """
  
      def indentation_rule():
          inst = Indentator(indent_str)
          return {'layout_handlers': {
              Indent: inst.layout_handler_indent,
              Dedent: inst.layout_handler_dedent,
              Newline: inst.layout_handler_newline,
              OptionalNewline: inst.layout_handler_newline_optional,
              OpenBlock: layout_handler_openbrace,
              CloseBlock: layout_handler_closebrace,
              EndStatement: layout_handler_semicolon,
          }}
      return indentation_rule