Module Output_method.Wrap_mode

This controls what happens when a single capture expression consumes multiple sexps
     during a single match. It specifies whether to wrap them together as a single sexp
     list or return all the results separately.

     For example:
     "(a %[.*])" tries to unwrap exactly one set of parens, match an 'a', and then
     capture all the sexps that follow that 'a'. Here are the three behaviors.

     Wrap_always:
     (a) -> Sexp.List []                                    (* () *)
     (a b) -> Sexp.List [ Sexp.Atom b ]                     (* (b) *)
     (a b c) -> Sexp.List [ Sexp.Atom b; Sexp.Atom c ]      (* (b c) *)

     Wrap_non_singletons:
     (a) -> Sexp.List []                                    (* () *)
     (a b) -> Sexp.Atom b                                   (* b *)
     (a b c) -> Sexp.List [ Sexp.Atom b; Sexp.Atom c ]      (* (b c) *)

     Unwrap_always:
     (a) -> []                                              (*  *)
     (a b) -> [ Sexp.Atom b ]                               (* b *)
     (a b c) -> [ Sexp.Atom b; Sexp.Atom c ]                (* b c *)

     This wrapping (or not) occurs before packing the result into whatever format
     specified by [Output_method.t] below.

     Since [Unwrap_always] has the possiblity of returning multiple sexps separately,
     the [`capture] type for it is a list of sexps instead of a single sexp.