ed to cast references
      rather than pointers. It is also the only cast that can be used to check whether
      a given interface is supported; in that case a return of 0 isn't an error condition.
    </p>
<p>
      <a name="polymorphic_pointer_cast"></a>While <code class="computeroutput">polymorphic_downcast</code>
      and <code class="computeroutput">polymorphic_cast</code> work with built-in pointer types only, <code class="computeroutput">polymorphic_pointer_downcast</code>
      and <code class="c