>key_of</a></span></dt>
<dt><span class="section"><a href="iterator/metafunctions/value_of_data.html">value_of_data</a></span></dt>
<dt><span class="section"><a href="iterator/metafunctions/deref_data.html">deref_data</a></span></dt>
</dl></dd>
</dl></div>
<p>
      Like <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a> and
      <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>,
      iterators are a fundamental concept in Fusion. As with <a href=