Untitled

$myHtml = <<<MARKUP
       <html>
           <head>
                <title>something</title></head>
           <body>
                <div>
                    <p>not valid</p>
                </div>
                <p>is valid</p>
                <p>is not valid</p>
                <p>is not valid either</p>
                <div>
                    <p>definitely not valid</p>
                </div>
           </body>
       </html>
MARKUP;

    $DomDocument = new DOMDocument();
    $DomDocument->loadHTML($myHtml);
    $DomXPath = new DOMXPath($DomDocument);
    $nodeList = $DomXPath->query('body/p');
    $yourNode = $DomDocument->saveHtml($nodeList->item(0));

    var_dump($yourNode);