- Blink exposes default values for pos in set and set size as 0. This is a legal value, but blink_ax_tree_source.cc checks for null-like (including 0) only sets the attribute for non-null.
- the heuristic used to calculate pos in set and set size if there are no such attributes is weak in Blink. A better heuristic is to calculate all items of the valid role on the same level in the accessibility tree under the container. It appears that we only consider the siblings of the current node and not its cousins.