
PASS Check the existence of Element.attachShadow
PASS Nodes other than Element should not have attachShadow
PASS Element.attachShadow must throw a TypeError if mode is not "open" or "closed"
PASS Element.attachShadow must create an instance of ShadowRoot
PASS Element.attachShadow must throw a NotSupportedError if the context object already hosts a shadow tree
PASS Element.attachShadow must throw a NotSupportedError for non-safelisted elements