pan> = 0;
<a name="l00296"></a>00296 
<a name="l00297"></a>00297   <span class="comment">// do parse and change the internal status, if failed, returns false</span>
<a name="l00298"></a>00298   <span class="keyword">virtual</span> <span class="keywordtype">bool</span> parse() = 0;
<a name="l00299"></a>00299 
<a name="l00300"></a>00300   <span class="comment">// return true if the context is empty</span>
<a name="l00301"></a>00301   <span class="keyword">virtual</span> <span class="keywordtype">bool</span> e