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A general description is here.
The ‘tcltk’ namespace can now be re-loaded after unloading.
The Tcl/Tk event loop is inhibited in a forked child from package ‘parallel’ (as in e.g. ‘mclapply()’).
On unix ‘Rscript’ will pass the ‘r_arch’ setting it was compiled with on to the R process so that the architecture of ‘Rscript’ and that of R will match unless overridden.