title: Use channel hiearchy of Boost.Log for severity and sink filtering
body: <p>I have been studying Boost.Log for a while and I believe now is the time for me to transition my code base from log4cxx to Boost.Log. I believe the design and implementation of Boost.Log will significantly improve my code maintenance and usage. I know the Boost.Log FAQ has a <a href="http://www.boost.org/doc/libs/1_60_0/libs/log/doc/html/log/rationale/why_not_log4j.html" rel="nofollow">page that says</a></p>
  
  <blockquote>
    <p>As for hierarchical loggers, there is no need for this feature in the current library design. One of the main benefits it provides in log4j is determining the appenders (sinks, in terms of this library) in which a log record will
    end up. This library achieves the same result by filtering.</p>
  </blockquote>
  
  <p>I understand the conceptual equivalence and am not trying to make Boost.Log into log4j/log4cxx. Rather my question is: How do I use Boost.Log to get the same functionality that I currently use from log4cxx? In particular, I want to set severity thresholds and sinks for specific nodes in a log source or channel hierarchy. For example, I have logging sources organized by <code>libA.moduleB.componentC.logD</code> with levels in the hierarchy separated by dots <code>.</code>. Using log4cxx one can set the overall threshold of <code>libA</code> to INFO with the more specific logger, <code>libA.moduleB</code>, having a threshold of DEBUG. </p>
  
  <pre><code>libA.threshold=INFO
  libA.moduleB.threshold=DEBUG
  </code></pre>
  
  <p>Similarly one can attach sinks to arbitrary nodes in the hierarchy. </p>
  
  <p>I believe that a similar capability is possible with Boost.Log but I need help/guidance on how to actually implement this. Plus, I am sure others who would like to transition to Boost.Log from other frameworks will have the same question. </p>
  
  <p>I sincerely appreciate your comments.</p>