docs: def _add_standard_attributes(cls):
          """Add attributes common to all state machines.
  
          These are methods for setting and checking state etc.
  
          """
          setattr(
              cls.context.new_class,
              cls.context.new_meta['state_attribute_name'],
              cls.context.state_value)
          setattr(
              cls.context.new_class,
              cls.context.state_name,
              utils.state_property)
  
          setattr(cls.context.new_class, 'is_', utils.is_)
          setattr(cls.context.new_class, 'can_be_', utils.can_be_)
          setattr(cls.context.new_class, 'set_', utils.set_)