code: func (i *IdentityMapping) ToContainer(pair Identity) (int, int, error) {
  	uid, err := toContainer(pair.UID, i.uids)
  	if err != nil {
  		return -1, -1, err
  	}
  	gid, err := toContainer(pair.GID, i.gids)
  	return uid, gid, err
  }
docs: // ToContainer returns the container UID and GID for the host uid and gid