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.

WWW: https://cran.r-project.org/web/packages/backports/