  <span class="identifier">value_type</span><span class="special">;</span>
   <span class="keyword">typedef</span>          <span class="keyword">const</span> <span class="identifier">value_type</span><span class="special">&amp;</span>                                       <span class="identifier">const_reference</span><span class="special">;</span>
   <span class="keyword">typedef</span>          <span class="identifier">const_reference</span>                                         <span class="identifier