n class="identifier">value_type</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">,</span> 
                        <span class="keyword">const</span> <span class="identifier">Ptree</span> <span class="special">&amp;</span><span class="special">,</span> <span class="keyword">bool</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">)</span><span class="special">;</span>
      <span class="keyword">template</span><span cla