$re = '/(?<=
<div>
(?:[^<]|<[^d]|<d[^i]|<di[^v]|<div[^>])*?
)
(?:[^<]|<[^d]|<d[^i]|<di[^v]|<div[^>])
(?=
(?:[^<]|<[^d]|<d[^i]|<di[^v]|<div[^>])*?
</div>
)/mx';
$str = '<div>< <span>Foo</span> ></div>
<div>< <span>Foo</span> v></div>
<div>< <span>Foo</span> iv></div>
<div>< <span>Foo</span> div></div>
<div>< <span>Foo</span> /div></div>
<div>< <span>Foo</span> </div></div>
<div><d <span>Foo</span> ></div>
<div><d <span>Foo</span> v></div>
<div><d <span>Foo</span> iv></div>
<div><d <span>Foo</span> div></div>
<div><d <span>Foo</span> /div></div>
<div><d <span>Foo</span> </div></div>
<div><di <span>Foo</span> ></div>
<div><di <span>Foo</span> v></div>
<div><di <span>Foo</span> iv></div>
<div><di <span>Foo</span> div></div>
<div><di <span>Foo</span> /div></div>
<div><di <span>Foo</span> </div></div>
<div><div <span>Foo</span> ></div>
<div><div <span>Foo</span> v></div>
<div><div <span>Foo</span> iv></div>
<div><div <span>Foo</span> div></div>
<div><div <span>Foo</span> /div></div>
<div><div <span>Foo</span> </div></div>
<div><div> <span>Foo</span> ></div>
<div><div> <span>Foo</span> v></div>
<div><div> <span>Foo</span> iv></div>
<div><div> <span>Foo</span> div></div>
<div><div> <span>Foo</span> /div></div>
<div><div> <span>Foo</span> </div></div>';
preg_match_all($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