| 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 | |