anchor.diff:          | MonoAndroid MonoAndroidVersion.V7 -> [ MonoAndroid MonoAndroidVersion.V6; DotNetStandard DotNetStandardVersion.V1_6 ]
           | MonoAndroid MonoAndroidVersion.V7_1 -> [ MonoAndroid MonoAndroidVersion.V7 ]
           | MonoAndroid MonoAndroidVersion.V8 -> [ MonoAndroid MonoAndroidVersion.V7_1 ]
  +        | MonoAndroid MonoAndroidVersion.V8_1 -> [ MonoAndroid MonoAndroidVersion.V8 ]
           | MonoTouch -> [ DotNetStandard DotNetStandardVersion.V1_6 ]
           | MonoMac -> [ DotNetStandard DotNetStandardVersion.V1_6 ]
           | Native(_) -> [ ]
  
positive.code:         | MonoAndroidVersion.V7    -> "7.0"
          | MonoAndroidVersion.V7_1   -> "7.1"
          | MonoAndroidVersion.V8   -> "8.0"
      override this.ToString() =
          match this with
          | MonoAndroidVersion.V1    -> "v1.0"
  
negative.code:         | "7.1" -> Some (MonoAndroidVersion.V7_1)
          | "8"
          | "8.0" -> Some (MonoAndroidVersion.V8)
          | "8.1" -> Some (MonoAndroidVersion.V8_1)
          | _ -> None
  
  [<RequireQualifiedAccess>]
  