Documentation Request Summary:

stepdown command no longer blocks writes while waiting for secondaries to catch up, instead writes will start failing with NotMaster immediately, but if no secondaries catch up within the secondary catch up time period then the node will step back up automatically and start accepting writes again.

Engineering Ticket Description:

Currently the stepdown command runs with the global lock in shared mode, which violates the concurrency rules for the _canAcceptNonLocalWrites variable.