postalAddress versus postalAddressAdditional

[Jens Wagner]

For the street address, 2 attributes have been defined (e.g. for home
address):

http://axschema.org/contact/postalAddress/home
http://axschema.org/contact/postalAddressAdditional/home

As I understand the Attribute Exchange Protocol, each attribute can
have a (ordered) list of values, e.g.

openid.ns.ax=http://openid.net/srv/ax/1.0
openid.ns.ax=fetch_response
openid.ax.type.address=http://axschema.org/contact/postalAddress/home
openid.ax.count.address=2
openid.ax.value.address.1=Main Street 123
openid.ax.value.address.2=Suite 456

should be valid.
What is the reason for the 'additional' attribue?

Best,
- jens