All timestamps are represented in the ISO 8601 format and in GMT. Dates in contact data are returned in a structured format.
identifies a resource version that was created after this one:
When updating or deleting resources, you need to provide etag of the local copy of the resource, so the API can perform a 3-way merge of data (if needed) or prevent deleting a resource if it has a newer etag.
All resource ids are strings. Contact ids and tag ids are unique.
Client-generated contact and tag ids must be uuids, but the API can return contact ids that are not in that format.