nt when the grammar gets quite complicated, it is desirable to
  visualize the parse traversal and see what's happening. There are some facilities
  in the framework that aid in the visualisation of the parse traversal for the
  purpose of debugging. The following macros enable these features.</p>
<a name="debugging_macros"></a>
<h2>Debugging Macros</h2>
<a name="spirit_assert_exception"></a>
<h3>BOOST_SPIRIT_ASSERT_EXCEPTION</h3>
<p> Spirit contains assertions that may activate when spirit is used incorrec