fier>implementation</span> <span class=identifier>defined</span></b> <span class=identifier>type</span><span class=special>;};</span>
  <span class=keyword>template</span><span class=special>&lt;</span><span class=keyword>typename</span> <span class=identifier>Tag</span><span class=special>&gt;</span>
  <span class=keyword>struct</span> <span class=identifier>index_iterator</span>            <span class=comment><b>// deprecated</b></span>
  <span class=special>{</span><span class=keyword>typedef</span> <b><