function is used to deprecate some behavior of a function.  It differs
    from L{warnings.warn} in that it is not limited to deprecating the behavior
    of a function currently on the call stack.

    @param function: The function that is being deprecated.

    @param warningString: The string that should be emitted by this warning.
    @type warningString: C{str}

    @since: 11.0
    é