Pp.AstSourceStable representation of Pp.t useful for serialization
type +'tag t = | Nop| Seq of 'tag t * 'tag t| Concat of 'tag t * 'tag t list| Box of int * 'tag t| Vbox of int * 'tag t| Hbox of 'tag t| Hvbox of int * 'tag t| Hovbox of int * 'tag t| Verbatim of string| Char of char| Break of string * int * string * string * int * string| Newline| Text of string| Tag of 'tag * 'tag tStable abstract syntax tree for Pp.t that can be used for serialization and deserialization.