19. The computer readable storage medium of claim 15 , wherein the at least one of the set of custom publication units that includes the additional content includes both the additional content and at least one of the copied, selected units of content.
19. The computer readable storage medium of claim 15 , wherein the at least one of the set of custom publication units that includes the additional content includes both the additional content and at least one of the copied, selected units of content. 20. The computer readable storage medium of claim 19 , wherein the additional content is specified by the user.