[dom] atomic tree actions (#174)

The spec need atomic actions for insert append and  replace into a tree. Should describe what it means in terms of child nodes and references to/from previous next sibling, with potential update of the parent first and last child. Then these can be references from insert and replace mutation algorithms. For the time being, these atomic actions are undefined.

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/174