A comment to the paragraph below was recently added via http://www.zope.org/Documentation/Books/ZopeBook/current/Security.stx#3-42
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Roles are similar to UNIX groups in that they abstract groups of
users. And like UNIX groups, Zope users can have more than one
role.
% Anonymous User - Sep. 22, 2002 3:06 pm:
/Zope users/each Zope user/