pan>
<span class="w">  </span><span class="p">}</span>

<span class="w">  </span><span class="c1">// Walk the tree.</span>
<span class="w">  </span><span class="nx">walk</span><span class="w"> </span><span class="p">(</span><span class="nx">accumulator</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w">    </span><span class="k">this</span><span class="p">.</span><span class="nx">stack</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><