Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
Note: This API is available only to WebExtensions.
 The Element.openOrClosedShadowRoot read-only property represents the shadow root hosted by the element, regardless if its mode is open or closed. 
 Use Element.attachShadow() to add a shadow root to an existing element.