Description:
------------
It seems like there's a bug when trying to set a value to the 'disabled' attribute using the DOMElement::setAttribute($name, $value) function.

Test script:
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<?php
$dom = new DOMDocument();

$a = $dom -> createElement('input');
$a -> setAttribute('disabled', 'ok');
$dom -> appendChild($a);

$b = $dom -> createElement('input');
$b -> setAttribute('disabled', 'somethingelse');
$dom -> appendChild($b);

$c = $dom -> createElement('input');
$c -> setAttribute('required', 'required');
$dom -> appendChild($c);

echo $dom ->saveHTML();
?>

Expected result:
----------------
<input disabled="disabled"><input disabled="somethingelse"><input required="required">

Actual result:
--------------
<input disabled><input disabled><input required="required">