pan></tt>
    taking instances of the types used in closures as their right operands are required.<br>
    <br>
    You may find an example of overloading the output operator for
    <tt><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></tt>
    in a <a href="faq.html#output_operator">related FAQ entry</a>.</td>
  </tr>
</table>

<p>By default, if the <tt>BOOST_SPIRIT_DEBUG</tt> macro is defined, all available
  debug output is generated. To fine tune the