code: func Reverse(u []byte) []byte {
  	// Special-case 16 bit UUIDS for speed.
  	l := len(u)
  	if l == 2 {
  		return []byte{u[1], u[0]}
  	}
  	b := make([]byte, l)
  	for i := 0; i < l/2+1; i++ {
  		b[i], b[l-i-1] = u[l-i-1], u[i]
  	}
  	return b
  }
docs: // Reverse returns a reversed copy of u.