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A general description is here.
R_PDFLATEXCMD is added to the environment variables set by 'R CMD' and is used by R CMD Rd2dvi.
R_LATEXCMD, R_PDFLATEXCMD, R_MAKEINDEXCMD and R_DVIPSCMD default to 'latex', 'pdflatex', 'makeindex' and 'dvips' respectively if no suitable executable was found at configure time (since they might well be available at run time, particularly for binary installations of R). This affects R CMD Rd2dvi and help(offline=TRUE).
R CMD Rd2dvi now gives an explicit error message if latex (or pdflatex) fails.
R CMD Rd2dvi gains a --no-index argument: processing some special characters on PDF indices gave errors which used to be ignored.