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After contacting their customer service with a written description, they asked for clarification, so I submitted a rough mockup - they replied with an invitation to sign a letter of understanding and submit to their marketing dept.
Mockup submitted to their marketing dept with the following description:
...plastic inserts could serve to enclose any side of each shelf so that one might use the shelving as a bookcase or as a container - perfect for students who don't want to deal with assembling wooden shelves which are heavy and expensive.
The slots in the diagram are probably too thick - the diagram is not exact, rather a simplified representation of adding plastic inserts via slots added to the boundaries of the shelving tiers, thereby allowing the shelves to be enclosed for the functionality of acting as bookshelves, as an enclosed container, etc. A thin insert will serve the purpose and maximize the available surface real estate.
I put your shelves into the closets of my office so the walls of the closet offer enclosure and serve as bookshelves.
The reason I love your shelves is that they are strong, lightweight and flexible - I have one tier left over with 4 legs and I use it in the office as a table top which can be broken down easily. They are like Legos - I can make them as tall or as low as I need.