GHC documentation of modules exposed by the base package

Dear all, By running in GHC 7.10.3 $ ghc-pkg field base-4.8.2.0 exposed-modules I can see various modules exposed by base-4.8.2.0 which are not documented (e.g. GHC.NUm) in http://downloads.haskell.org/~ghc/7.10.3/docs/html/libraries/index.html Which is the criterion for adding GHC documentation to the modules exposed by base? All the best, -- Andrés