[keystone] Need clarification about Stein policies

The Keystone policy.json file I created with oslo-policy-generator contains lines I don't understand. For example /list_users/. The comment says:

# DEPRECATED "identity:list_users":"rule:admin_required" has been # deprecated since S in favor of "identity:list_users":"(role:reader # and system_scope:all) or (role:reader and # domain_id:%(target.domain_id)s)".

I do understand the expression starting with (role:reader .... , but contrarily to the comment, the policy is

"identity:list_users": "rule:identity:list_users"

This looks like a circular definition, and in any case, nowhere do I seerule:identity:list_users defined.

Can someone in the know explain how this policy is processed?

Thanks much,

Bernd