I tried this:

{-# LANGUAGE TypeFamilies #-}

class C x where
  type A x

It fails with this error:

Temp/jhc1.hs:4   - Error: parse error at "}"

Standalone type families don’t work either:

{-# LANGUAGE TypeFamilies #-}

type family A x

Temp/jhc1.hs:3   - Error: parse error at "family"

Is there an example somewhere that I missed while googling?