t least a complete 
    // forward_iterator interface (not shown here)
</span><span class="keyword">        typedef</span> std::forward_iterator_tag iterator_category;

<span class="comment">    // additional requirements
</span>        <a href="class_reference_lexer.html#member_functions">lex_iterator</a>();

        <span class="keyword">template</span> &lt;<span class="keyword">typename</span> Iterator&gt;
        <a href="class_reference_lexer.html#constructor">lex_iterator</a>(Iterator <span class="key