comparison customization
  <custom-comparison>`.

Instances of this class are frequently used for introspection purposes
like:

- `fields` returns a tuple of them.
- Validators get them passed as the first argument.
- The :ref:`field transformer <transform-fields>` hook receives a list of
  them.

.. versionadded:: 20.1.0 *inherited*
.. versionadded:: 20.1.0 *on_setattr*
.. versionchanged:: 20.2.0 *inherited* is not taken into account for
    equality checks and hashing anymore.
.. versionadded:: 21.1.0 *eq_key* and *order_key*

For the full version history of the fields, see `attr.ib`.
)