An administrator can either be a full administrator who can access everything in the server prefs, and all users, or you can delegate administration and control what an admin can do to some degree.

There are two different checkboxes. One for "Everything" and one for "Limited". If you enable the "Limited" checkbox, the user who logs in to do remote admin will only get the user manager interface.

The user manager will only contain a list of users who are part of a group that matches their username exactly. So if test2 is a limited admin, there must be a group named "test2". The test2 group should not have test2 as a member, or else test2 can edit himself.

Security is enforced when the admin goes to save a change to a user. The server verifies any change the remote admin submits.

1.) If the user is not a member of the group, the change is rejected.

2.) If the home folders being specified are not a sub folder of the home directory that the admin can access, the change is rejected.

3.) If the change involves adding an event to a user that specifies a "plugin" action, the change is rejected.

These are done to enforce security and prevent privilege escalation.