The step timing functions jump-both, jump-none, jump-start and jump-end were introduced to the spec for easing functions in 2018. Two of these (jump-start and jump-end) are aliases for start and end. The remaining two provide increased flexibility for step transitions by enabling step functions in which both or neither endpoint has a discontinuous step. Previously, one and only one of the two endpoints could have a step discontinuity.
This feature provides support for a richer set of step animations. Firefox already has support for jump-* step timing functions. Adding support in Chromium improves cross-browser interoperability.
Docs: https://drafts.csswg.org/css-easing-1/#step-easing-functions
Samples: https://wpt.fyi/results/web-animations/timing-model/time-transformations/transformed-progress.html https://wpt.fyi/results/css/css-transitions https://wpt.fyi/results/css/css-easing
Explainers: https://danielcwilson.com/blog/2019/02/step-and-jump/ https://developer.mozilla.org/en-US/docs/Web/CSS/animation-timing-function