parentNode() inspected only the immediate parent, which caused three
spec deviations:
- With currentNode at root, the `parent !== this.root` guard did not
fire (parent is root's OWN parent), so a node OUTSIDE the walker's
subtree was returned — createTreeWalker(root).parentNode() yielded
<body>. A TreeWalker must never surface a node above its root.
- The same guard excluded root as a *result*, so when currentNode's
accepted ancestor was root itself, parentNode() returned null instead
of root.
- A skipped (or otherwise non-accepted) immediate parent ended the
search rather than continuing up to the first accepted ancestor.
Replaced with the DOM 6.1 algorithm: climb from currentNode, returning
the first ancestor that filters to FILTER_ACCEPT, with the loop's
`node !== this.root` guard keeping the walk inside root while still
letting root be returned. Reuses the three-valued `_filter` from #461.
Last of the TreeWalker mover deviations, after nextNode (#461),
previousNode (#462) and the child/sibling movers (#469).
Andrey Mnatsakanov
845abb96f7