$re = '~(?:(?![^<>]*(?:>))[^<])+~';
$str = 'das is<C strike ><c1>t ein text </c1></C><C u ><c1>der </c1></C><C b u ><c1>hier </c1></C>im <C i u ><c1>editor </c1></C><u></u>steht';
preg_match_all($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