$re = '/(~(?(?=.*?~~.*?~).*?~.*?~.*?~|[^~]+?~))/';
$str = '~The ~spectacle~~ was ~borken~, but that was not the same ~spectacle~
that was given to ~me~.';
preg_match_all($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