This property returns a string which contains the postal code
associated with the area where the IP address is located. In the
United States, this is a 5-digit numeric code. In Canada, this will
contain the forward sortation area (the first three characters of the
six character postal code). Local delivery portions of a postal code
(such as the ZIP+4 code in the United States, or the local delivery
unit in Canada) are not included.
This information will be most accurate within the geographic
region of North America. Postal codes are locale specific, and this
property may return an empty string if the postal code for the
location cannot be determined.