code: func (u UUID) Variant() uint {
  	switch {
  	case (u[8] & 0x80) == 0x00:
  		return VariantNCS
  	case (u[8]&0xc0)|0x80 == 0x80:
  		return VariantRFC4122
  	case (u[8]&0xe0)|0xc0 == 0xc0:
  		return VariantMicrosoft
  	}
  	return VariantFuture
  }
docs: // Variant returns UUID layout variant.