Consider merging https://chromium.googlesource.com/chromium/blink/+/56504cf75d798cf192c25fbcbfff15213b72bcab Implement cloneNode for Document When cloning HTMLDocument and SVGDocument we need to ensure that we create a new HTMLDocument and SVGDocument respectively. http://dom.spec.whatwg.org/#dom-node-clonenode
> HTMLDocument and SVGDocument Blink still doesn't have MathML? *** This bug has been marked as a duplicate of bug 11646 ***