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A general description is here.
R CMD INSTALL has a new option --data-compress to control the compression used when lazy-loading data. One new option isNew possibilities are --data-compress=bzip2 which will give ca 15% better compression at the expense of slower installation times. Also, and --data-compress=xz, often giving even better compression on large datasets at the expense of much longer installation times. (The latter is used for the recommended packages: it is particularly effective for 'survival'.)
file() for open = "", "r" or "rt" will automagically detect compressed files (from gzip, bzip2 or xv). This means that compressed files can be specified by file name to (rather than via a gzfile() connection) to read.table(), readlines(), scan() and so on.
The 'type' argument of index.search() is deprecated: there are no longer directories of types other than 'help'.
Having a version of 'tar' capable of automagically detecting compressed archives is useful for utils::untar(), and so 'gtar' (a common name for GNU tar) is preferred to 'tar': set environment variable TAR to specify a particular 'tar' command.
R CMD replaced TEXINPUTS rather than appending to it (as documented and intended).