Optional ReadonlydurationSeconds this leg takes. Required unless spring supplies one.
Optional ReadonlyeaseThe timing curve for this leg alone. Mutually exclusive with spring.
Optional ReadonlyholdSeconds to rest at to before the next step begins.
Optional ReadonlyspringPhysics for this leg instead of a curve, supplying its own duration.
A from or to here is refused: the step already defines its range, and
the spring is driven over 0..1 so the physics stays independent of the
units. Dropping them silently would animate to a value nobody asked for.
The type says so as well as the assertion sequence runs, so the refusal
arrives at the keystroke rather than at the call.
ReadonlytoWhere this leg ends. It begins wherever the previous one finished.
One leg of a sequence. The start is wherever the previous leg finished.