The bar at index, the replay clock's "now". Null when there is no data.
Under intra-bar replay this is the partial bar as it stands this step, not the completed one, which is what makes it the right thing to drive a host's own forming volume bar or an OHLC readout from.
0-based newest bar; -1 before the first observation in timed replay.
True while the newest bar forms along a simulated path (simulate), because
no finer bar covers it. Its forming prices were never traded, so a host shows
that plainly; the bar closes on the real bar either way.
Multiplier over barMs: 2 plays two bars per barMs.
Which step of the forming bar this is, 0-based, and how many it takes. Both
are 0 and 1 without subBars, so a transport that shows them needs no
special case for the plain mode.
Bars in the replay set (the scrub bar's maximum is total - 1).
Everything a transport bar and a clock need, in one object.