[Rd] cross-platform portable code in CRAN Repository Policy

[Da Zheng]

Hello,

I'm trying to submit my package to CRAN. When I read the policy, it says:
Package authors should make all reasonable efforts to provide
cross-platform portable code. Packages will not normally be accepted
that do not run on at least two of the major R platforms.

What major R platforms does this policy refer to?
Currently, my package runs in Ubuntu. If it works on both Ubuntu and
Redhat, does it count as two platforms?

Thanks,
Da