Confirmed for windows 10 registry editor. However, when i disable "Guess object position information when unavailable", position information is not announced. This means that NVDA has to guess based on a particular algorithm, and that algorithm fails here.

I'm leaning towards a won't fix. @jcsteh, thougths?

This only occurs in the 64 bit registry editor; I just tested it with the 32 bit version and it works as expected. We can map from an IAccessible child id to an HTREEITEM (so this must be CommCtrl >= 6). At a guess, I'd say bits are being truncated from the 64 bit handle when the response comes back as 32 bit in this case.

This doesn't explain why this works just fine in, say, Device Manager. My only guess is that there aren't as many nodes (and the tree isn't as dynamic), so we don't end up with 64 bit handles. Regardless, we would definitely hit this 64 bit truncation problem at some point.

This will either need the SendMessage part of #3339 or perhaps we can use UIA for all 64 bit SysTreeView32 controls.

CC @michaelDCurran.

cc: @Robert-J-H, @ABuffEr

For 64 bit, the mapping function is not implemented. I've consulted the UIA source code. They are essentially traversing the children, almost the same as we do.
However, the procedure is highly inefficient.
for each focus change (e.g. arrowing around), the position under the parent is being enumerated and likewise the total number of children (similar items in group).
There are possible solutions for this.

1. caching. Should be valid for as long as accChildCount stays the same (it returns all children seen so far, not just those on one level, i.e. it changes only if a level is freshly expanded, collapsing doesn't reset the counter.)

2. Make an initial guess through the location. The difference between parent and next parent divided by the item height gives an approximation of the total amount of children. the accessibleChildren function (oleacc) can return all IDs for that range, it is trivial to apply accValue (gives the tree level) in order to count the objects at the same level as the focused item.

3. limit the enumeration to at most xxx elements or given time out (Narrator seems to do that).
   However, this issue is at any rate a duplicate, we've discussed something along these lines elsewhere.

I am closing also this one in favor of #7041 because the discussion goes much further in detail on that issue. Thanks.