Grid vs Flexbox Animations

MDN identifies grid properties as allowing discrete animation, but what does that mean? And how does it compare to flexbox (which allows continuous animation "as each of the properties of the [ flex ] shorthand")?

Grid Expand Animation (Discrete)

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Grid properties such as grid-column accept the animation properties, but do not backfill transitions between states

Flexbox Expand Animation (Continuous)

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Flex Box properties flex-grow , flex-shrink , and flex-basis accept the animation properties as well as backfill any transitions between states.