PostalInfo::info_type can be an enum

[nrempel]

https://datatracker.ietf.org/doc/html/rfc5733#section-3.2.1

One or two contact:postalInfo elements that contain postal-
address information. Two elements are provided so that address
information can be provided in both internationalized and
localized forms; a "type" attribute is used to identify the two
forms. If an internationalized form (type="int") is provided,
element content MUST be represented in a subset of UTF-8 that can
be represented in the 7-bit US-ASCII character set. If a
localized form (type="loc") is provided, element content MAY be
represented in unrestricted UTF-8. The contact:postalInfo
element contains the following child elements:

[djc]

Ah, that's a a good bit more complex than what we have now. So if I understand correctly:

• There might be two postalInfos, not just one (as we have now)
• If type = int the content must be representable in ASCII
• If type = loc the content may use all of UTF-8