e><div class="info">
<code class="code"><span class="constructor">Callback</span>.register_exception n exn</code> registers the
   exception contained in the exception value <code class="code">exn</code>
   under the name <code class="code">n</code>. C code can later retrieve a handle to
   the exception by calling <code class="code">caml_named_value(n)</code>. The exception
   value thus obtained is suitable for passing as first argument
   to <code class="code">raise_constant</code> or <code class="code">