anchor.diff:  
   and flag =
     | Private
  -  | NoExtract
  +  | WipeBody
     | CInline
     | Substitute
     | GCType
     | Comment of string
  +  | MustDisappear
   
   and fsdoc = string
   
  
positive.code: (** Versioned binary writing/reading of ASTs *)
  
  type version = int
  let current_version: version = 25
  
  type file = string * program
  type binary_format = version * list<file>
  
negative.code: and translate_flags flags =
    List.choose (function
      | Syntax.Private -> Some Private
      | Syntax.NoExtract -> Some WipeBody
      | Syntax.CInline -> Some CInline
      | Syntax.Substitute -> Some Substitute
      | Syntax.GCType -> Some GCType
  