constructing the conntent; 2) conventional approaches to constructing the content, with a twist; 3) new (novel) approaches to constructing content; and, 4) radical approaches - staying within the framework guidelines - that set new standards, and stimulate completelt new ways to think about content.
In fact, a testbook project could "live beside itself", in parallel, as many different potential 'products; and/or, once it gets going, begins to take on a 'flavor' or demeanor' that resonates with certain contributors.
This is one beauty of open sourcing K-12 content, in that it permits conent innovation around a basic structure, and can organically evolve in a way that fills the needs of people beyond the original "textbook content" intention. Really, a K-12 'textbook' in geometry, authored by wickipedia, could be one part (or the core, whichever) of a massive project that fills many needs, outside the initial mandate of the project.
University texts can be treated somewhat differently; there, one can dispense with preceding structure, and 'go for it'. If the material is compelling, people will use it. Unfortunately, this is not the case at K-12. (but open source can slowly help to change that; in fact, *only* open source can change that...certainly, the commercial publishers never will).
Sanford