Reference.Extension
type t = [
| `Resolved of Paths.Reference.Resolved.Extension.t |
| `Root of string * [ `TExtension | `TException | `TUnknown ] |
| `Dot of Paths.Reference.LabelParent.t * string |
| `Extension of Paths.Reference.Signature.t * Names.ExtensionName.t |
| `Exception of Paths.Reference.Signature.t * Names.ExceptionName.t |
]