* submodules ( http://www.cs.utah.edu/plt/publications/gpce13-f-color.pdf )
* Languages as modules (i.e. the #lang mechanism ) ( http://www.ccs.neu.edu/racket/pubs/pldi11-thacff.pdf )
* Documentation system that links identifiers to documentation (respecting the scope)
( http://docs.racket-lang.org/ )