OptionallimitOptionalonlySkip every Anfrage the corpus holds with all its documents, without a request for it; what is missing, or stored without a document, is handled.
OptionalperiodOptionalrefsHandle only these references of the window, and the ones they were filed under
before (DocRef.formerly). With retryFailed too, either one selects.
OptionalretryHandle only the Anfragen whose last attempt failed (SourceState.failed).
OptionalsinceOptionaluntil
The part of the sync options that says what a job covers: the window discovery looks at, and which of the Anfragen it finds are handled (issue #27).