Primary key values (as concatenated strings) of records that have been deleted. Format uses CompositeKey.ToConcatenatedString() - e.g., "ID|abc123" or "Field1|val1||Field2|val2" These should be removed from the client's cache.
Records that have been created or updated since the client's maxUpdatedAt. These should be merged into the client's cache, replacing any existing records with the same primary key.
Differential update data containing only changes since the client's cached state. Used to efficiently update client caches without transferring the entire dataset.