code: private static int spliceIn(ByteBuffer src, ByteBuffer dest) {
      int position = dest.position();
      int srcPos = src.position();
      dest.put(src);
      src.position(srcPos);
      return position;
    }
docs: Write the contents of src to dest, without messing with src's position.
  
  @param dest (position is advanced)
  @return the pos in dest where src is written