Postcode or Area Code or Zipcode
I would like to add an additional requirement for the address data set. In the UK we called it postcode, it is a 9 digit field. This is used for sorting post and it plays a big part for marketing and send out mailshots.
In Malaysia, it is an area code for now. E.g 58200 is for Puchong, Kuala Lumpur, Malaysia.
If your future CSS form builder upgrades could take this into consideration, your product will be more useful. For example, integrating this form with royal mail's postcode addressing system.