This is simply the notion that a user should be able to produce different bindings of a document on the fly.
For example, if the user is reading The Future of Text, which is a large work, they may want to produce a version which only includes certain articles, or they may want to have all the volumes of the book in one binding, to be able to do searches and views across all the volumes in one go.
The idea is that this can then be shared in whatever way a user wants, and the recipient can choose to expand or reduce the binding to suit them.