假设我在字符串中有一个HTML块:
<div class="nav mainnavs">
<ul>
<li><a id="nav-questions" href="/questions">Questions</a></li>
<li><a id="nav-tags" href="/tags">Tags</a></li>
<li><a id="nav-users" href="/users">Users</a></li>
<li><a id="nav-badges" href="/badges">Badges</a></li>
<li><a id="nav-unanswered" href="/unanswered">Unanswered</a></li>
</ul>
</div>
如何解析HTML并计算特定类型标记的实例数,例如<div>或<li>？