James' comment:

5.6.3.3. Implied reverse relations for IAccessible2 and ATK

"""
In the case of role="treeitem", when aria-owns is not used, user agents SHOULD do the following:

If the current treeitem uses aria-level, then walk backwards in the tree until a treeitem is found with a lower aria-level, then set RELATION_NODE_CHILD_OF to that element. If the top of the tree is reached, then set RELATION_NODE_CHILD_OF to the tree element itself.
If the parent of the treeitem has a role of group, then walk backwards from the group until an element with a role of treeitem is found, then set RELATION_NODE_CHILD_OF to that element.
In the case of aria-atomic:

User agents SHOULD check the chain of ancestor elements for aria-atomic="true". If found, user agents SHOULD set the RELATION_MEMBER_OF relation to point to the ancestor that sets aria-atomic="true".
"""

It's inappropriate for the UAIG to have a normative section for specific APIs. The section should be titled simply, "Implied reverse relations", the prose should be more generic with defined terms like "child relationship" and "member relationship" and, where appropriate, there should be a table that defines what the keys are in any particular API (RELATION_NODE_CHILD_OF and RELATION_MEMBER_OF)