Optional ReadonlychecksumThe target's §33 checksum after the step — present only while ReplayPlayer.verifyChecksums is on. See that property for the cost.
ReadonlyresimulatingWhether this step was part of a ReplayPlayer.seekToStep re-simulation rather than ordinary playback. A UI that renders every step can skip the fast-forward by ignoring these.
ReadonlystepIndex of the step that just ran — the same index its inputs were recorded
under (§34). The first step of a recording is 0, and
ReplayPlayer.currentStep is step + 1 when the listener runs.
What ReplayPlayer.onStep receives after each replayed fixed step.