MAINT: Possibly hide functions which shouldn't be called by users

[HaoZeke]

If the users are not supposed to be calling the lower level functions, do they need to be exported, and thus being part of the public user interface of the package? It could be less confusing possibly if only those functions are exported which are meant to be called directly by users.

First noted here: ropensci/software-review#606 (comment)

[HaoZeke]

Response from here: ropensci/software-review#606 (comment)

I thought about this, but decided not to mainly because downstream package users (including me for other dependent packages) would want to call these functions where it makes sense (e.g. if my downstream package will only write matrix data or sparse matrix data) and CRAN disallows / warns calling unexported functions via :::