php使用自带dom扩展进行元素匹配的原理解析

libxml_use_internal_errors(true);

$dom = new \DOMDocument;
$content = htmlspecialchars_decode($content);
libxml_use_internal_errors(true);
$content = mb_convert_encoding($content, 'HTML-ENTITIES', 'UTF-8');
$dom->loadHTML($content);

$a = $dom->getElementsByTagName('a');
$p = $dom->getElementsByTagName('p');

$elements = $dom->getElementsByTagName('a');
foreach ($elements as $element) {
  $element->textContent = '替换成其它的文字';
}

<div>
<p>
<a href="xxx" rel="external nofollow" >我是文字</a>
</p>
<p>
内容替换
</p>
</div>

$elements = $dom->getElementsByTagName('p');
foreach ($elements as $element) {
  if($element->hasChildNodes()){
    $element->textContent = 'p标签内容替换';
  }
}

function hasChild($element, $tags)
{
  foreach($tags as $v){
  $elements = $element->getElementsByTagName($v);

  if($elements->length){
  return true;
  }

  }
  return false;
}
$tags = array('title','h1','h2','h3','h4','h5','a','p','dd','img');  

$elements = $dom->getElementsByTagName('p');
foreach ($elements as $element) {
  if(hasChild($element, $tags)){
    $element->textContent = 'p标签内容替换';
  }
}