icl\iterator.hpp and icl\detail\element_iterator.hpp include <boost/config/warning_disable.hpp>. This disabled the MSVC warning C4996 without re-enabling it again.
For context: C4996 is MSVC's warning for using deprecated stuff. This means code that uses Boost.Icl will not get warning C4996 which IMO is quite bad. <boost/config/warning_disable.hpp> even contains the following comment:
// IT SHOULD NOT BE INCLUDED BY ANY BOOST HEADER.
//
// YOU SHOULD NOT INCLUDE IT IF YOU CAN REASONABLY FIX THE WARNING.