Implementations of functions which have been introduced in R since version 3.0.0. The backports are conditionally exported which results in R resolving the function names to the version shipped with R (if available) and uses the implemented backports as fallback. This way package developers can make use of the new functions without worrying about the minimum required R version.
.valid.factor()for R versions prior to 3.4.0.
...elt()for R versions prior to 3.5.0.
isFALSE()for R versions prior to 3.5.0.
import(). This is now the recommended way to use backports non-interactively. Simply importing backports in the NAMESPACE still works, but is comparably error-prone if the same library is used by multiple R installations.
get0()for R versions prior to 3.2.0.
hasName()for R versions prior to 3.4.0.
file.info()with backport for argument
file.mode()for R versions prior to 3.2.0.