<header>Primary group</header>
This is the group that by default will own any files or processes
created by this user. If this user attempts to access a file and the group
of that file is the user's primary group then the group permissions for that
file will apply (unless the user is the owner of the file). <p>

If you are editing an existing user and the primary group is changed,
the <a href=chgid>Change group ID on files?</a> option determines what
files (if any) have their group changed. <p>
<hr>