From the MPL standpoint, all iterators are opaque types. Incrementing,
dereferencing and the rest of iterator functionality is accessed
through the associated iterator metafunctions.
.. copyright:: Copyright � 2001-2009 Aleksey Gurtovoy and David Abrahams
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)