anchor.diff:  
     SoundEffectStream play(
       SoundEffect sound,
  -    [Object tag,
  -      bool loop = false,
  +    [bool loop = false,
         double volume = 1.0,
         double pitch = 1.0,
         double pan = 0.0,
  
positive.code:     // Create new PlayingSound object
      SoundEffectStream playingSound = new SoundEffectStream(
        sound,
        tag,
        loop,
        volume,
        pitch,
  
negative.code: class SoundEffectStream {
    SoundEffectStream(
      this.sound,
      this.loop,
      this.volume,
      this.pitch,
  