This blog is updated daily.
A general description is here.
Namespace importing is more careful about warning on masked generics, thanks to a patch by Yohan Chalabi.
The help pages, including ?regexp, have been updated and should be consulted for details of the new implementations.
A different regular expression engine is used for basic and extended regexps and also for approximate matching. This is based on the TRE library of Ville Laurikari, a modifed copy of which is included in the R sources.
This is often faster, especially in a MBCS locale.
KSome known differences are that it is less tolerant of invalid inputs in MBCS locales, and conforms more strictly to the POSIX standard in its interpretation of incorrect regexps such as "^*"in its interpretation of undefined (extended) regexps such as "^*". Also, the interpretation of ranges such as [W-z] in caseless matching is no longer to map the range to lower case.
This engine may in future be used in 'literal' mode for fixed = TRUE, and there is a compile-time option in src/main/grep.c to do so.
The use of repeated boundary regexps in gsub() and gregexpr() as warned about in the help page does not work in this engine (it did in the previous one since 2005).
The algorithm used by strsplit() has been reordered to batch by elements of 'split': this can be much faster where regexps are usedfor fixed = FALSE (as multiple compilation is avoided).
clearNames() ('stats') is deprecated for unname().