code: func (b *Batch) MakePicture(p Picture) TargetPicture {
  	if p != b.cont.Picture {
  		panic(fmt.Errorf("(%T).MakePicture: Picture is not the Batch's Picture", b))
  	}
  	bp := &batchPicture{
  		pic: p,
  		dst: b,
  	}
  	return bp
  }
docs: // MakePicture returns a specialized copy of the provided Picture that draws onto this Batch.