- var_dump: documentation ( source)
- array_combine: documentation ( source)
- preg_match_all: documentation ( source)
<?php
$data = 'BUTTONSOURCE[18]=AngellEYE_PHPClass&VERBOSITY[4]=HIGH&ParamNoLength=PlainTextIsItAnArray&ParamNoLengthUrlEncoded%3DEncodedTextIsItAnArray&%3CParam42_URLEncodedWithSpecialChars%3E%3DThisIs42%21';
preg_match_all('/([^=&]+)\=([^=&]+)/', $data, $result);
$result = array_combine($result[1], $result[2]);
var_dump($result);