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A general description is here.
Quartz draws contiguous lines much faster
The use of embedded nuls in character strings is deprecated: They will no longer be allowed in R 2.8.0.
merge() failed if there were no common columns and one of the inputs had zero rows.
expand.grid() failed if an input had length 0.
match() does again truncate strings at embedded nuls (as newly documented in 2.7.0).
The vertical scrollbar on the data editor/viewer now works when scrolling beyond 65535 rows. (PR#11291)