consider the keys of the mapping
            rather than the values or the key-item pairs.
          </dd>
        </dl>
      </dd>
    </dl>
    
<h3> <a name="indexing_suite_subclasses"></a>indexing_suite sub-classes</h3>
    <p>
      The <tt>indexing_suite</tt> is not meant to be used as is. A couple of
      policy functions must be supplied by subclasses of
      <tt>indexing_suite</tt>. However, a set of <tt>indexing_suite</tt>
      subclasses for the standard indexable STL containers will be provi