Regulární výraz který vybere div s class="content"*

$string = '<div class="content">Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industrys standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in<p> the 1960s with the release of</p> <div id="neco">Letraset sheets containing Lorem Ipsum passages, and more recently</div> with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</div><div class="out">Já jsem div, který už ve svém textu mít nechci, ale stejně tam neustále je a nevím proč.</div>';

preg_match('/<div class="content">(.+)<\/div>/', $string, $matches);
var_dump($matches);

preg_match('/<div class="content">(.+)<\/div>/U', $page, $matches);