Using source subdirectories within R packages with roxygen2

Question

I would like to use a directory structure within the R folder for the source code of a package. For example, within my R folder I have an alg

Answer 1

Writing R Extensions has this to say (in Section 1.1.5) about subdirectories under the R directory:

The R and man subdirectories may contain OS-specific subdirectories named unix or windows.

Implied in this is that they can't have other subdirectories other than those two. This is confirmed in an r-devel thread and again later in another r-devel thread.