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A general description is here.
Assignment of an environment to functions or as an attribute to other objects now works for S4 subclasses of ‘"environment"’.
‘!’ dropped attributes such as names and dimensions from a length-zero argument. (PR#14424)
The Fortran code used by ‘nls(algorithm = "port")’ could infinite-loop when compiled with high optimization on a modern version of ‘gcc’, and ‘SAFE_FFLAGS’ is now used to make this less likely. (PR#14427, seen with 32-bit Windows using ‘gcc 4.5.0’ used from R 2.12.0.)
Additional utilities now work correctly with S4 subclasses of ‘"environment"’ (‘rm’, locking tools and active bindings).
Reading a package's ‘CITATION’ file now defaults to ASCII rather than Latin-1: a package with a non-ASCII ‘CITATION’ file should declare an encoding in its ‘DESCRIPTION’ file and use that encoding for the ‘CITATION’ file.
There are several small changes to output which ‘zap’ small numbers, e.g. in printing quantiles of residuals in summaries from ‘"lm"’ and ‘"glm"’ fits, and in test statistics in ‘print.anova()’.
‘system(intern = TRUE)’ and ‘pipe()’ connections are guaranteed to be available on all builds of R.
Changing both line texture and line cap (end) resulted in the latter to be omitted form the PDF code. In addition, line cap (end) and join are now set explicitly in PDF output to ensure correct defaults.
‘available.packages()’ by default only returns information on the latest versions of packages whose version requirements are satisfied by the currently running R.
A different regular expression engine is used for basic and extended regexps and is also for approximate matching. This is based on the TRE library of Ville Laurikari, a modified copy of which is included in the R sources.
This is often faster, especially in a MBCS locale.
Some known differences are that it is less tolerant of invalid inputs in MBCS locales, and 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.