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A general description is here.
The ‘plot’ method for ‘lm’ and ‘glm’ fits, ‘plot.lm()’, gets a new option ‘iter.smooth’ with a default of ‘0’ for binomial fits, no longer downweighting when smoothing the residuals.
Source package installation can be ‘staged’: this is currently optional but intended to become the default before release. In a staged install the package is installed into a temporary location under the final library directory and moved into place once the installation is complete. The benefit is that partially-installed packages are hidden from the view of other R sessions.
The overall default is set by environment variable ‘R_INSTALL_STAGED’. ‘R CMD INSTALL’ has new options ‘--staged-install’ and ‘--no-staged-install’, and packages can use the ‘StagedInstall’ field in their ‘DESCRIPTION’ file to opt in or (more likely) out.