This blog is updated daily.
A general description is here.
‘R CMD build’ by default uses the internal method of ‘tar()’ to prepare the tarball. This is more likely to produce a tarball compatible with ‘R CMD INSTALL’ and ‘R CMD check’: an external ‘tar’ program, including options, can be specified _via_ the environment variable ‘R_BUILD_TAR’.
‘R CMD check --as-cran’ notes assignments to the global environment and calls to ‘attach()’.