Include non-CRAN package in CRAN package

Question

The question is pretty simple. First:

1. Is it possible to include a non-CRAN (or bioconductor, or omega hat) package in a CRAN package and actually use tools f

Answer 1

Its possible, but! ...

There is a field in the DESCRIPTION file that that you can use:

Additional_repositories: http://ghrr.github.io/drat

BUT!

Everything that depends on the functionality from the package from the additional repository has to be absolutely optional.

So packages from this repo should be placed under Suggests.

Example

I am not 100% sure whether or not BioConductor and OmegaHat are considered mainstream or not.