Q:

How see documentation for tools:::.check_packages()

When running 
R CMD check 

a file called check is executed, which contains
# ${R_HOME}/bin/check -*- sh -*- for checking add-on packages

args=
while test -n "${1}"; do
  args="${args}nextArg${1}"
  shift
done

## NB: Apple's ICU needs LC_COLLATE set when R is started.
echo 'tools:::.check_packages()' | R_DEFAULT_PACKAGES= LC_COLLATE=C "${R_HOME}/bin/R" --no-restore --slave --args ${args}

Note tools:::.check_packages() from above
I have tried to find documentation for this function from RStudio, but cannot seem to find it using ?tools:::.check_packages() and I cannot determine why?
Also, there is no tools package among those listed here, presumably because tools comes with base R. Is there somewhere to find the tools' package documentation?
Note also that the ::: means it's a non-exported function, and the . means it's hidden. But I'm not sure how these affect documentation 

A:

Not all functions come with documentation, especially if they are not exported and are meant to be used internally. You'll have to figure out how the function works following how it actually looks like. You can still see documentations for an exported function such as
?tools::add_datalist

and you can still see the function form for .check_packages by 
tools:::.check_packages

The base packages are not listed in CRAN---for example, base, stats, graphics... anything that you see as "attached base packages" in sessionInfo(). 

