 versioned.  So one might
want to specify:
<pre><code>
BOOST_CLASS_IMPLEMENTATION(nvp&lt;T&gt;, boost::serialization::level_type::object_serializable)
BOOST_CLASS_TRACKING(nvp&lt;T&gt;, boost::serialization::track_never)
</code></pre>
Examination of the definition of these macros reveals that they won't expand
to sensible code when used with a template argument.  So rather than using the
convenience macros, use the original definitions
<pre><code>
template&lt;class T&gt;
struct implementation_level&lt;nvp&l