Main module missing haddock

As a newcomer to CAD (but not to Haskell), the haddock pages leave much to be desired. For example, what is this `R` parameter to all of the `write` functions? It's completely undocumented. Diving into the source suggests it's some sort of resolution, but I'm unsure if I should be giving it big or small values. A good rule of thumb is that every function and non-obvious parameter exported by the main module should have haddock.