PHP过滤HTML标签

<?php$content = '<div class="content"><div class="content"><div class="content"><span class="blue">发布</span><pre>谷歌的这个功能</pre></div><span class="blue">5发布</span>谷歌</div><span class="blue">发布</span>谷歌</div><span></span>百度';//$str = htmlspecialchars_decode($content);$str =  html_entity_decode($content);var_dump($str);?>

有一些并不是能很好的过滤掉