What is the purpose of "A" palettes in Radix Colors?

[averybuehler]

For example, what is the difference between tomato and tomatoA? I can see that the A palette is using hsla and thus has an opacity to it, but I'm still confused. It's not documented what the A means or when the A palette should be used (as compared to the regular palette). What confuses me more is that all of the A1 colors have the same value: hsla(0, 0%, 0%, 0) (black with 0% opacity). On the website, however, it appears that each of them is used on top of another color.

Can someone please clarify:

1. What the purpose of the A color palettes are?
2. When should we be using the A color palette based on the documentation?
3. Why are all A1 values identical?

[benoitgrelard]

The A variants are alpha variants. This means that essentially they are to be used on top of background that may vary in colours.
They have been created in a way that makes them remain as close as possible to the original color but with baked-in alpha.