On Hackage, there seems to be no documentation for GHC.IO.Exception in base, but the package can in fact be imported so it's not exactly an internal package. directory and likely many other packages do use the GHC-specific error types like InappropriateType in exceptions, so it would be useful if there were a documentation page for these things even if there isn't any text. As it is right now, the discoverability of these error types is very low as you need to know the magical URL to show the source code: https://hackage.haskell.org/package/base/docs/src/GHC.IO.Exception.html That's also partly a problem with Haddock; AFAIK there's no way to navigate to the Source Code packages of modules whose documentation is disabled, even though they are in fact present if you can figure out the URL. So would it be OK to open up this module or is there a reason for keeping them discreet?