In Gilmore, for RHEL 8, RH124, Chapter 7, Section 1, Linux File-system Permissions, there is this:
I'm guessing that the ??? is supposed to reference the grahic which follows the paragraph (Example group membership to facilitate collaboration).
It is a link, which points to:
(file:///C:/Users/gotht/Desktop/Red Hat/New Course/RHEL8_RH124/html/ch07.html#img-perms-users-and-groups)
A collaborative learning environment, enabling open source skill development.