(will be found through Argument Dependent Lookup) or [within an
    anonymous namespace] within <tt><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span></tt>,
    so it is visible where it is called.<br>
    <br>
    <img src="theme/alert.gif"> Note in particular that when <tt>BOOST_SPIRIT_DEBUG_FLAGS_CLOSURES</tt>
    is set, overloads of <tt><span class="identifier">operator</span><span class="special">&lt;&lt;</s