def areaBetween(requestContext, *seriesLists):
    """
    Draws the vertical area in between the two series in seriesList. Useful for
    visualizing a range such as the minimum and maximum latency for a service.

    areaBetween expects **exactly one argument** that results in exactly two
    series (see example below). The order of the lower and higher values
    series does not matter. The visualization only works when used in
    conjunction with ``areaMode=stacked``.

    Most likely use case is to provide a band within which another metric
    should move. In such case applying an ``alpha()``, as in the second
    example, gives best visual results.

    Example::

      &target=areaBetween(service.latency.{min,max})&areaMode=stacked

      &target=alpha(areaBetween(service.latency.{min,max}),0.3)&areaMode=stacked

    If for instance, you need to build a seriesList, you should use the
    ``group`` function, like so::

      &target=areaBetween(group(minSeries(a.*.min),maxSeries(a.*.max)))
    """
    if len(seriesLists) == 1:
        [seriesLists] = seriesLists
    assert len(seriesLists
        ) == 2, 'areaBetween series argument must reference *exactly* 2 series'
    lower, upper = seriesLists
    if len(lower) == 1:
        [lower] = lower
    if len(upper) == 1:
        [upper] = upper
    lower.options['stacked'] = True
    lower.options['invisible'] = True
    upper.options['stacked'] = True
    lower.name = upper.name = 'areaBetween(%s)' % upper.pathExpression
    return [lower, upper]
