code: func xorBitmapRun(a, b *Container) *Container {
  	statsHit("xor/BitmapRun")
  	output := a.Clone()
  
  	for _, run := range b.runs() {
  		output.bitmapXorRange(uint64(run.start), uint64(run.last)+1)
  	}
  
  	return output
  }
docs: // xorRunRun computes the exclusive or of a bitmap and a run container.