...
(Fedora Implementation Note: This is a slight departure from the W3C's description of WebAC, where the object of the acl:agent property must be a URI. We chose to implement it in such a way that the WebAC authorization module supports both String Literals and URIs in order to ease the integration with existing authentication or single-sign-on systems that identify users with string usernames. See ACL Agents - Strings vs. URIs for further details.)
However, listing individual users this way can get unwieldy, so you can also use the acl:agentClass property to specify a group of users:
...