For any futures contract at the CME, under "Margins" tab, we can see a table like the one below.
My question is: what are the two columns named "Start Period" and "End Period"? Does it represent maturity months of futures contracts, or levels of maintenance margin for all futures in future periods? For example, does it mean that the Jun 2022 RBOB futures have a maintenance margin of 10,750 USD but the Jul 2022 RBOB futures have a maintenance margin of 10,000 USD? Or does it mean that all RBOB futures will have a maintenance margin of 10,750 USD from May 2022 to June 2022 and it will be 10,000 USD in July 2022?