$re = '/^label (\S+)(?!.*(?:\n(?!label).*)*?\n[ \t]*\[end_timeline\])/m';
$str = 'label Colorcode (Object)
Dialog
Speaker: "Text"
Speaker 2: "[i]Text[/i]! [pause={pause.medium}] more text."
do function_name("parameter", {parameter})
# comment, there are no inline-comments
[end_timeline]
label Maroon (Guitar)
Speaker: "Text"
[end_timeline]
label Pink (Chest)
Speaker: "Text"
label Königsblau (Wardrobe)
Speaker: "Text"
Speaker: "Text"
Speaker: "Text"
[end_timeline]
label Azur (Sorcerers Hat)
Speaker: "Text"
# [end_timeline]
label Jade (Paintings)
Speaker: "Text"
label Gras (Ship in a Bottle)
Speaker: "Text"
Speaker: "Text"
[end_timeline]
label Goldgelb (Golden Apple)
Speaker: "Text"
[end_timeline]
label Himmelblau (Helmet)
Speaker: "Text"
Speaker: "Text"
Speaker: "Text"
Speaker: "Text"';
preg_match_all($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