def experimental(fn):
    """Mark a pethod as experimental. Interface or implementation of an
    experimental method might very likely change. Use with caution. This
    decorator just appends a doc string."""
    warning = """
    .. warning::

       This method is experimental. Interface or implementation might
       change. Use with caution and note that you might have to modify
       your code later.
    """
    if fn.__doc__ is not None:
        fn.__doc__ += warning
    fn._bubbles_experimental = True
    return fn
