code: func (c *Container) WriteTo(w io.Writer) (n int64, err error) {
  	if c.isArray() {
  		return c.arrayWriteTo(w)
  	} else if c.isRun() {
  		return c.runWriteTo(w)
  	} else {
  		return c.bitmapWriteTo(w)
  	}
  }
docs: // WriteTo writes c to w.