PHP如何去掉HTML标签？

<?php
$text = '<p>Test paragraph.</p><p><span>立即学习</span>“<a href="https://pan.quark.cn/s/7fc7563c4182" style="text-decoration: underline !important; color: blue; font-weight: bolder;" rel="nofollow" target="_blank">PHP免费学习笔记（深入）</a>”；</p><!-- Comment --> <a href="#fragment">Other text</a>';
echo strip_tags($text);
echo "\n";
// 允许 <p> 和 <a>
echo strip_tags($text, '<p><a>');
?>

Test paragraph. Other text
<p>Test paragraph.</p><p><span>立即学习</span>“<a href="https://pan.quark.cn/s/7fc7563c4182" style="text-decoration: underline !important; color: blue; font-weight: bolder;" rel="nofollow" target="_blank">PHP免费学习笔记（深入）</a>”；</p> <a href="#fragment">Other text</a>

<?php
function strip_tags_content($text, $tags = '', $invert = FALSE) {

  preg_match_all('/<(.+?)[\s]*\/?[\s]*>/si', trim($tags), $tags);
  $tags = array_unique($tags[1]);
   
  if(is_array($tags) AND count($tags) > 0) {
    if($invert == FALSE) {
      return preg_replace('@<(?!(?:'. implode('|', $tags) .')\b)(\w+)\b.*?>.*?</\1>@si', '', $text);
    }
    else {
      return preg_replace('@<('. implode('|', $tags) .')\b.*?>.*?</\1>@si', '', $text);
    }
  }
  elseif($invert == FALSE) {
    return preg_replace('@<(\w+)\b.*?>.*?</\1>@si', '', $text);
  }
  return $text;
}
?>

<?php
function stripUnwantedTagsAndAttrs($html_str){
  $xml = new DOMDocument();
//Suppress warnings: proper error handling is beyond scope of example
  libxml_use_internal_errors(true);
//List the tags you want to allow here, NOTE you MUST allow html and body otherwise entire string will be cleared
  $allowed_tags = array("html", "body", "b", "br", "em", "hr", "i", "li", "ol", "p", "s", "span", "table", "tr", "td", "u", "ul");
//List the attributes you want to allow here
  $allowed_attrs = array ("class", "id", "style");
  if (!strlen($html_str)){return false;}
  if ($xml->loadHTML($html_str, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD)){
    foreach ($xml->getElementsByTagName("*") as $tag){
      if (!in_array($tag->tagName, $allowed_tags)){
        $tag->parentNode->removeChild($tag);
      }else{
        foreach ($tag->attributes as $attr){
          if (!in_array($attr->nodeName, $allowed_attrs)){
            $tag->removeAttribute($attr->nodeName);
          }
        }
      }
    }
  }
  return $xml->saveHTML();
}