Description:
------------
To conform to the XML spec, DOMElement::setAttributeNS() [and other related methods like DOMDocument::createAttributeNS(), etc] incorrectly allows @xml:space='foo'.

See the related bug (https://bugs.php.net/bug.php?id=74988) for the details on WHY this should not be allowed.



Test script:
---------------
libxml_use_internal_errors( true );
libxml_clear_errors();
$dom = new DOMDocument();
$root = $dom->createElement( 'root' );
$root->setAttributeNS( 'http://www.w3.org/XML/1998/namespace', 'xml:space', 'foo' );
$errs = libxml_get_errors();
$dom->appendChild( $root );
$xml = $dom->saveXML();
var_dump( $errs );
var_dump( $xml );

Expected result:
----------------
Either:

    DOMElement::setAttributeNS() [and other related methods like DOMDocument::createAttributeNS(), etc) should return false and libxml_get_errors() should report the well-formedness error

or

    DOMElement::setAttributeBS() should return true but just ignore setting the attribute and it's value.


Actual result:
--------------
array(0) {
}
string(46) "<?xml version="1.0"?>
<root xml:space="foo"/>
"