PCD content is organized into units, which are semantic objects (such as iView, page and role) whose parent hierarchy consists only of plain folders. A unit includes the semantic object's complete child hierarchy, and the semantic object is called the root of the unit.
For example, a page in a folder in the top-level Portal Content folder is a unit, but an iView in the page or a delta link of the page in a role are not units.
Many tasks can only be performed on units and not on objects within a unit. The following features apply only to unit objects:
Permissions: Only unit objects and plain folders have access control lists (ACLs). Objects inside a unit object inherit their ACLs from the unit object.
Delta Links: Delta links can only be created from unit objects.
Transport: Only unit objects can be transported.
Translation: Translation worklists include only unit objects.
Caching: Only unit objects can be cached.