BOOST_VMD_ELEM macro, which by default just returns an element of a sequence,
        has a usage where you can have it return both the element and the remaining
        part of the sequence after the element, or even just the remaining part of
        the sequence after the element by itself. This offers a form of splitting
        the sequence on a particular element. When used to return the remaining part
        of a sequence the remaining data may subsequently be treated as a VMD sequence
        again