Currently location always implicitly stored as __location property. It breaks paradigm of not enforcing tree format in parse5. It makes sense to introduce treeAdapter.setNodeLocationInfo method that will give implementers opportunity to decide how to store it.
Another thing that bothered for a long time is the name of the __location property. Since where will be a major version bump due to the changes in the location info layout required for error reporting feature I guess it's a good chance to rename it to location.