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A general description is here.
grep[l], [g]sub and [g]regexpr now work in bytes in an 8-bit locales if there is no marked UTF-8 input string: this will be somewhat faster, and for [g]sub() give the result in the native encoding rather than in UTF-8 (which was the behaviour prior to R 2.10.0).
A new argument 'skipCalls' has been added to browser() so that it can report the original context when called by other debugging functions.
[g]regexpr(pattern, fixed = TRUE) returned match positions in bytes (not characters) in an MBCS locale if 'pattern' was a single byte.
[g]sub(fixed = TRUE) with a single-byte pattern could conceivably have matched part of a multibyte character in a non-UTF-8 MBCS.
findLineNum() and setBreakpoint() would sometimes fail if the specified file was not in the current directory.
[g]sub() could use excessive stack space when used with a very long vector ofcontaining some non-ASCII data.