IE11 cloneNode behaves unexpectedly

[daffl]

It turns out that text nodes containing text with a - will be turned into several text nodes in IE11:

var frag = document.createDocumentFragment();
var text = document.createTextNode('some-text');

frag.appendChild(text);

var clone = frag.cloneNode(true);

// clone.childNodes.length -> 3 instead of 1

Due to this we have to fall back to the less performant node cloning already used in IE 9 and 10 for now.

Possible optimizations could be to re-consolidate multiple adjacent text nodes if they initially contained a - (also see Node.normalize).

[phillipskevin]

I found that cloneNode only behaves incorrectly after we set up a MutationObserver on the documentElement.

var frag = document.createDocumentFragment();
var text = document.createTextNode('some-text');
var observer = new MutationObserver(function(mutations) {});

frag.appendChild(text);

var clone = frag.cloneNode(true);
// clone.childNodes.length -> 1

observer.observe(document.documentElement, { childList: true, subtree: true });
clone = frag.cloneNode(true);
// clone.childNodes.length -> 3