$re = '/
(*SKIP)(*FAIL)|[^&\r\n]+(?:&(?!#xA;)[^&\r\n]*)*/';
$str = 'The client requires photos of a radioactive world
Reach the target planet.
The client requires photos.

Reach the target planet.
The client requires photos of a desert world
Reach the target planet.
The client requires photos of an airless world. Reach the target planet.
The client requires photos of a strange world

Reach the target planet
Make a quick scan.
The disturbed region must be accessed by <SPECIAL>Portal<>
Speak to the inhabitants of the Space Anomaly to learn more" to "&;A&;&;&;
A';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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