  Our <code class="computeroutput"><span class="identifier">on_success</span></code> handler gets
        a reference to the actual <code class="computeroutput"><span class="identifier">position_cache</span></code>
        and calls its <code class="computeroutput"><span class="identifier">annotate</span></code> member
        function, passing in the AST and the iterators. <code class="computeroutput"><span class="identifier">position_cache</span><span class="special">.</span><span class="identifier">annot