HTMLTemplateElement: shadowRootSerializable property

The shadowRootSerializable property reflects the value of the shadowrootserializable attribute of the associated <template> element.

Note that this property is not useful for developers. If a <template> element is used to declaratively create a ShadowRoot, then this object and property do not exist. Otherwise, if an HTMLTemplateElement is created, the value of this property is irrelevant because the object is not a shadow root and cannot subsequently be changed to a shadow root.