 <span class="keyword">class</span> <span class="identifier">Expr</span> <span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">my_expr</span><span class="special">;</span>

<span class="keyword">struct</span> <span class="identifier">my_domain</span>
  <span class="special">:</span> <a class="link" href="boost/proto/domain.html" title="Struct template domain">proto::domain</a><span class="special">&lt;</span> <a class="link" href="boost/proto/pod_generator.html" titl