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A general description is here.
axis() has new arguments 'col.ticks' and 'lwd.ticks' to allow the colour and line width of ticks to be set separately from that of the line (e.g. to set one or the other to transparent or zero width).
legend() has a new argument 'box.col' to set the colour of the enclosing box.
legend() gains a 'xpd' argument to make it easier to place a legend in the margins or outer margins.
stripchart() now passes '...' to title() (as well as to plot.default() and axis()). (Wish of PR#12202)
The automatic placement of legend() with 'title' and a reversed 'x' axis was incorrect. (PR#12019)
pchisq(x, df=0) was always one even for x < 0; similarly for pgamma(x, alpha=0).
add1() and drop1() now return a P-value of NaN in cases with df=0 for test="Chisq" (they gave NaN until pchisq was altered in R 2.6.2).
The default methods of drop1() and add1() now re-evaluate in the object's formula environment, rather than simply in the parent (informal bug report by Werner Stahel).
The undocumented limit of 8191 bytes on comments (from # to the end of the line) in R code has been removed.
edit.data.frame() not longer fails if called on a 0-column data frame and no column is created.
The automatic placement of legend() with 'title' and a
reversed 'x' axis was incorrect. (PR#12019)