ationError.path` is shorter) are considered better matches,
    since they indicate "more" is wrong with the instance.

    If the resulting match is either :validator:`oneOf` or :validator:`anyOf`,
    the *opposite* assumption is made -- i.e. the deepest error is picked,
    since these validators only need to match once, and any other errors may
    not be relevant.

    Arguments:
        errors (collections.Iterable):

            the errors to select from. Do not provide a mixture of
            errors from different validation attempts (i.e. from
            different instances or schemas), since it won't produce
            sensical output.

        key (collections.Callable):

            the key to use when sorting errors. See `relevance` and
            transitively `by_relevance` for more details (the default is
            to sort with the defaults of that function). Changing the
            default is only useful if you want to change the function
            that rates errors but still want the error context descent
            done by this function.

    Returns:
        the best matching error, or ``None`` if the iterable was empty

    .. note::

        This function is a heuristic. Its return value may change for a given
        set of inputs from version to version if better heuristics are added.
    N)