undefined:</p>
<ul>
  <li>on an unsuccessful match </li>
  <li>when an attempt to copy or assign from another match object with an incompatible 
    attribute type (e.g. <tt>match&lt;std::string&gt;</tt> from <tt>match&lt;int&gt;</tt>).</li>
</ul>
<h3>The match class:</h3>
<pre><span class=keyword>    template </span><span class=special>&lt;</span><span class=keyword>typename </span><span class=identifier>T</span><span class=special>&gt;
</span><span class=keyword>    class </span><span class=identifier>mat