[boost] [mpl] Possible documentation bug

The MPL Reference Manual page for at_c: http://www.boost.org/libs/mpl/doc/refmanual/at-c.html Contains the following sample code: typedef range_c<long,10,50> range; BOOST_MPL_ASSERT_RELATION( (at_c< range,0 >::value), ==, 10 ); BOOST_MPL_ASSERT_RELATION( (at_c< range,10 >::value), ==, 20 ); BOOST_MPL_ASSERT_RELATION( (at_c< range,40 >::value), ==, 50 ); Does at_c<unspecified>::value exist? I get a compilation error: error: `value' is not a member of type `boost::mpl::at_c<range, 0> '