Description:
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DOMElement::setAttribute() allows one to specify a colon in the attribute name, for example "xsi:type". If an attribute with a matching namespace prefix and local name already exists in the element, the creation of the new attribute will cause two identically-named attributes to exist in the same element.


Reproduce code:
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$dom = DOMDocument::loadXML("<root xmlns:somens='uri://bla'><element somens:foo='bar' /></root>");

print $dom->firstChild->firstChild->setAttribute('somens:foo', 'baz');

print $dom->saveXML();

Expected result:
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DOMElement::setAttribute() should return FALSE or throw an exception; the DOMDocument should not be changed.


Actual result:
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<?xml version="1.0"?>
<root xmlns:somens="uri://bla"><element somens:foo="bar" somens:foo="baz"/></root>