anchor.diff:  
           /// Run the emitter.
           abstract Run : int64 -> Constraint -> Emitter * Output
  +
  +        /// Convert the emitted particles to a ParticlesDescriptor.
  +        abstract ToParticlesDescriptor : int64 -> ParticlesDescriptor
   
       /// Transforms a particle value.
       type 'a Transformer =
  
positive.code: 
      /// Describes the life of an instance value.
      /// OPTIMIZATION: LifeTimeOpt uses 0L to represent infinite life.
      /// OPTIMIZATION: avoids use of Liveness type to avoid its constructor calls.
      type [<NoEquality; NoComparison; Struct>] Life =
          { StartTime : int64
            LifeTimeOpt : int64 }
  
negative.code:             member this.Run time constrain =
                  let (emitter, output) = Emitter<'a>.run time constrain this
                  (emitter :> Emitter, output)
              member this.ToParticlesDescriptor time =
                  this.ToParticlesDescriptor time this
              end
  
      /// A particle system.
  