easy once we understand
      how to register an identifier subset. The only particular thing to realize
      is that the type of any v-type is the v-type BOOST_VMD_TYPE_TYPE. So our subset
      register of our new v-type BOOST_VMD_TYPE_UDEF_SHAPES is:
    </p>
<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_VMD_SUBTYPE_REGISTER_BOOST_VMD_TYPE_UDEF_SHAPES</span> <span class="special">(</span><span class="identifier">BOOST_VMD_TYPE_TYPE</span><span class