what does it mean by could be both/neither? how about the example here, I assume

|

specifies a

or

relationship otherwise

sysprefix/user:*

would totally invalidates the existence of writing

sysprefix/user

ahead of it

definition sysprefix/user {}

definition sysprefix/resource {
    /**
     * viewer can be granted to a specific user or granted to *all* users.
     */
    relation viewer: sysprefix/user | sysprefix/user:*
}