i>
  <li>when its value is set through the <tt>value(val)</tt> member function</li>
  <li> if it is assigned or copied from a compatible match object (e.g. <tt>match&lt;double&gt;</tt> 
    from <tt>match&lt;int&gt;</tt>) with a valid attribute. A match object <tt>A</tt> 
    is compatible with another match object <tt>B</tt> if the attribute type of 
    <tt>A</tt> can be assigned from the attribute type of <tt></tt> <tt>B</tt> 
    (i.e. <tt>a = b;</tt> must compile).</li>
</ul>
<p>The match attribute is 