$re = '/[pP]([a-zA-Z0-9 +-]|(%20)){13,}0000/';
$str = 'PLX000000000PQ50000
pLX000000000PQ50000
plx000000000pq50000
PLX-0000-0000-0PQ5-0000
PLX-0000-0000-0PQ50000
PLX+0000+0000+0PQ5+0000
PLX%200000%200000%200PQ5%200000
PLX 0000 0000 0PQ5 0000';
preg_match_all($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