impressed by cabal init's template comments

foo.cabal

-- The package version.  See the Haskell package versioning policy (PVP)         
-- for standards guiding when and how versions should be incremented.            
-- http://www.haskell.org/haskellwiki/Package_versioning_policy                  
-- PVP summary:      +-+------- breaking API changes                             
--                   | | +----- non-breaking API additions                       
--                   | | | +--- code changes with no API change                  
version:             0.1.0.0