1. Yes, true. The element `elem.lastChild` is always the last one, it has no `nextSibling`.
2. No, wrong, because `elem.children[0]` is the first child *among elements*. But there may exist non-element nodes before it. So `previousSibling` may be a text node.

Please note: for both cases if there are no children, then there will be an error.

If there are no children, `elem.lastChild` is `null`, so we can't access `elem.lastChild.nextSibling`. And the collection `elem.children` is empty (like an empty array `[]`).
