type <code>Pred</code>, we say that <code>q</code>
is <i>serialization-compatible</i> with <code>p</code> if
<blockquote>
<code>p(x,y) == q(x',y')</code>
</blockquote>
for every <code>x</code> and <code>y</code> of type <code>T</code> and <code>x'</code> and
<code>y'</code> being restored copies of <code>x</code> and <code>y</code>,
respectively.
</p>

Operation: saving of a <code>multi_index_container</code> <code>m</code> to an
output archive (XML archive) <code>ar</code>.

<blockquote>
<b>Requires:</b> <