code: func GetPreference(o dhcp6.Options) (Preference, error) {
  	v, err := o.GetOne(dhcp6.OptionPreference)
  	if err != nil {
  		return 0, err
  	}
  
  	var p Preference
  	err = (&p).UnmarshalBinary(v)
  	return p, err
  }
docs: // GetPreference returns the Preference Option value, as described in RFC 3315,
  // Section 22.8.
  //
  // The integer preference value is sent by a server to a client to affect the
  // selection of a server by the client.