OptionalCRON_minimum gap between cron firings; see DEFAULT_CRON_INTERVAL_MS
OptionalCRON_overrides maxMs
OptionalCRON_overrides maxRows
OptionalCRON_overrides maxUnits
OptionalDRUPAL_on by default; 0 turns it off for a site that wants nothing running in the background
the levers cron reads from the environment