DiscoverContextURL performs a DNS-based CardDAV service discovery as described in RFC 6352 section 11.

Filter returns the filtered list of address objects matching the provided query.

Match reports whether the provided AddressObject matches the query.

Client provides access to a remote CardDAV server.

Handler handles CardDAV HTTP requests.

SyncQuery is the query struct represents a sync-collection request.

SyncResponse contains the returned sync-token for next time.

Backend is a CardDAV server backend.

PreconditionType as defined in https://tools.ietf.org/rfcmarkup?doc=6352#section-6.3.2.1.