On selector for multiple architectures (OR, not AND)

I build a snap for armhf, arm64 and x64. I had this and it worked to download Rustc only on arm64:

  - on arm64:
    - rustc

Now I want it on armhf too, but reading on the grammar of the selector:

The body of the on clause is taken into account if every (AND, not OR) selector is true

So if I try on arm64,armhf: the statement will simply be ignored, right? Is there a standard way to do that?

Not having used this particular part of the snapcraft feature set, I think you can just have

- on arm64:
  - rustc
- on armhf:
  - rustc

Although apologies if that does not work, I just had a look at the text and I didn’t use it in my own snaps.