a>.
          With help of <a href="http://www.boost.org/doc/libs/release/libs/phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a>
          and <a class="link" href="../detailed/expressions.html#log.detailed.expressions.attr" title="Generic attribute placeholder">expression placeholders</a>
          we can construct a formatter that will extract the attribute value and
          pass it along with the target stream to the <code class="computeroutput"><span class="identifier">point_formatter</span