OK, that's clear. Thanks.
Re. the new field, if I create a field called new_field associated with a contact, am I right that I use the addCustomField method in PHP and Contact as the customFieldType?
Once I've added the field, can I just pass the new data whenever I create/update a contact and is it automatically returned whenever I retrieve a contact record or do I have to do something special to create, update or retrieve it?