y default, if <code class="computeroutput">
          <a class="link" href="extends.html" title="Struct template extends">proto::extends&lt;&gt;</a></code> has not been used
          to associate a domain with an expression.</p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a c