Description:
------------
Echoing $dom->saveXML() for a freshly created DOMDocument usually yields an XML declaration, even if the DOMDocument constructor is passed a bogus XML version parameter. However, nothing (not even an error message) is printed if I pass a bogus encoding parameter.

If PHP checks to make sure that the encoding parameter is correct, then shouldn't it also check to make sure the version is correct?

Reproduce code:
---------------
$hi = new DOMDocument();
echo $hi->saveXML();
echo "\n";
$hi = new DOMDocument('1.0', 'utf-8');
echo $hi->saveXML();
echo "\n";
$hi = new DOMDocument('3.14', 'utf-8');
echo $hi->saveXML();
echo "\n";
$hi = new DOMDocument('3.14', 'lkj');
echo $hi->saveXML();
echo "\n";

Expected result:
----------------
<?xml version="1.0"?>
<?xml version="1.0" encoding="utf-8"?>
<?xml version="3.14" encoding="utf-8"?>
<?xml version="3.14" encoding="lkj"?>

Actual result:
--------------
<?xml version="1.0"?>
<?xml version="1.0" encoding="utf-8"?>
<?xml version="3.14" encoding="utf-8"?>
/* Nothing printed for the last line. */