$re = '/(?(DEFINE)
(?<void>br|img|area|base|col|command|embed|hr|input|keygen|link|meta|param|source|track|wbr|!DOCTYPE)
(?<any>[^<>]*+)
)
<div \s class="card">
(?P<pair> (?&any)
(:?
<(?P<v_tag>(?!\/)(?&void))(?&any)> (?:(?&pair) | (?&any))*+ (<\/(?P=v_tag)>)? |
<(?P<tag>(?!\/)[^<> ]++)(?&any)> (?:(?&pair) | (?&any))*+ <\/(?P=tag)>
) (?&any)
)*
<\/div>/mx';
$str = '<!DOCTYPE html>
<html>
<head>
<title>Example</title>
</head>
<body>
<div class="card-container">
<div class="card">
<h5>First MD Card</h5>
<img src="https://mdbootstrap.com/img/Photos/Horizontal/Nature/4-col/img%20(34).jpg" alt="Card image cap">
<p>
Lorem ipsum dolor sit amet consectetur adipisicing elit. Sapiente
fugiat accusamus excepturi rem temporibus nobis natus.
</p>
</div>
<div class="slider">
<ul class="progress-bar">
<li class="active"></li>
<li></li>
<li></li>
</ul>
</div>
</div>
</body>
</html>
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php