code class="computeroutput"><span class="identifier">Attr</span></code> is the
                      The type of the original attribute to be used as the key into
                      the symbol generator. <code class="computeroutput"><span class="identifier">T</span></code>
                      is the data type associated with each key.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" clas