% -*- coding: utf-8 -*-
\newcommand{\Rlogo}{\if{html}{\figure{../../html/Rlogo.svg}{options: class="toplogo" alt="[R logo]"}}\if{latex}{\figure{Rlogo.pdf}{options: width=0.5in}}}

\name{NEWS}
\title{R News}
\encoding{UTF-8}

\section{\Rlogo CHANGES IN R 4.1.2}{
  \subsection{C-LEVEL FACILITIES}{
    \itemize{
      \item The workaround in headers \file{R.h} and \file{Rmath.h}
      (\code{using namespace std;}) for the Oracle Developer Studio
      compiler is no longer needed now C++11 is required so has been
      removed.  A couple more usages of \code{log()} (which should have
      been \code{std::log()}) with an \code{int} argument are reported on
      Solaris.

      \item The undocumented limit of 4095 bytes on messages from the
      S-compatibility macros \code{PROBLEM} and \code{MESSAGE} is now
      documented and longer messages will be silently truncated rather
      than potentially causing segfaults.

      \item If the \code{R_NO_SEGV_HANDLER} environment variable is
      non-empty, the signal handler for SEGV/ILL/BUS signals (which
      offers recovery user interface) is not set. This allows more
      reliable debugging of crashes that involve the console.
    }
  }

  \subsection{DEPRECATED AND DEFUNCT}{
    \itemize{
      \item The legacy S-compatibility macros \code{PROBLEM},
      \code{MESSAGE}, \code{ERROR}, \code{WARN}, \code{WARNING},
      \code{RECOVER}, \dots{} are deprecated and will be hidden in \R
      4.2.0. \R{}'s native interface of \code{Rf_error} and
      \code{Rf_warning} has long been preferred.
    }
  }

  \subsection{BUG FIXES}{
    \itemize{
      \item \code{.mapply(F, dots, .)} no longer segfaults when
      \code{dots} is not a \code{list} and uses \code{match.fun(F)} as
      always documented; reported by Andrew Simmons in \PR{18164}.

      \item \code{hist(<Date>, ...)} and \code{hist(<POSIXt>, ...)}
      no longer pass arguments for \code{rect()} (such as \code{col} and
      \code{density}) to \code{axis()}.  (Thanks to Sebastian Meyer's
      \PR{18171}.)

      \item \verb{\Sexpr{ch}} now preserves \code{Encoding(ch)}. (Thanks to
      report and patch by Jeroen Ooms in \PR{18152}.)

      \item Setting the RNG to \code{"Marsaglia-Multicarry"} e.g., by
      \code{RNGkind()}, now warns in more places, thanks to
      André Gillibert's report and patch in \PR{18168}.

      \item \code{gray(numeric(), alpha=1/2)} no longer segfaults, fixing
      \PR{18183}, reported by Till Krenz.

      \item Fixed \code{dnbinom(x, size=<very_small>, .., log=TRUE)}
      regression, reported by Martin Morgan.

      \item \code{as.Date.POSIXlt(x)} now keeps \code{names(x)}, thanks to
      Davis Vaughan's report and patch in \PR{18188}.

      \item \code{model.response()} now strips an \code{"AsIs"} class typically,
      thanks to Duncan Murdoch's report and other discussants in \PR{18190}.

      \item \code{try()} is considerably faster in case of an error and
      long call, as e.g., from some \code{do.call()}.  Thanks to
      Alexander Kaever's suggestion posted to R-devel.

      \item \code{qqline(y = <object>)} such as \code{y=I(.)}, now works,
      see also \PR{18190}.

      \item Non-integer \code{mgp} \code{par()} settings are now handled
      correctly in \code{axis()} and \code{mtext()}, thanks to Mikael
      Jagan and Duncan Murdoch's report and suggestion in \PR{18194}.

      \item \code{formatC(x)} returns length zero \code{character()} now,
      rather than \code{""} when \code{x} is of length zero, as documented,
      thanks to Davis Vaughan's post to R-devel.

      \item \code{removeSource(fn)} now retains (other) \code{attributes(fn)}.
    }
  }
}

\section{\Rlogo CHANGES IN R 4.1.1}{
  \subsection{NEW FEATURES}{
    \itemize{
      \item \code{require(\var{pkg}, quietly = TRUE)} is quieter and in
      particular does not warn if the package is not found.
    }
  }

  \subsection{DEPRECATED AND DEFUNCT}{
    \itemize{
      \item Use of \samp{ftp://} URIs should be regarded as
      deprecated, with on-going support confined to \code{method =
	"libcurl"} and not routinely tested.  (Nowadays no major browser
      supports them.)

      \item The non-default \code{method = "internal"} is deprecated for
      \samp{http://} and \samp{ftp://} URIs for both
      \code{download.file} and \code{url}.

      \item On Windows, \code{method = "wininet"} is deprecated for
      \samp{http://}, \samp{https://} and \samp{ftp://} URIs for both
      \code{download.file} and \code{url}.  (A warning is only given for
      \samp{ftp://}.)

      For \samp{ftp://} URIs the default method is now \code{"libcurl"}
      if available (which it is on \acronym{CRAN} builds).

      \code{method = "wininet"} remains the default for \samp{http://}
      and \samp{https://} URIs but if \code{libcurl} is available, using
      \code{method = "libcurl"} is preferred.
    }
  }

  \subsection{INSTALLATION}{
    \itemize{
      \item \command{make check} now works also without a LaTeX
      installation.  (Thanks to Sebastian Meyer's \PR{18103}.)
    }
  }

  \subsection{BUG FIXES}{
    \itemize{
      \item \command{make check-devel} works again in an \R build
      configured with \option{--without-recommended-packages}.

      \item \code{qnbinom(p, size, mu)} for large \code{size/mu} is correct
      now in a range of cases (\PR{18095}); similarly for the \code{(size,
      prob)} parametrization of the negative binomial.  Also \code{qpois()}
      and \code{qbinom()} are better and or faster for extreme cases.  The
      underlying C code has been modularized and is common to all four cases
      of discrete distributions.

      \item \code{gap.axis} is now part of the \code{axis()} arguments which
      are passed from \code{bxp()}, and hence \code{boxplot()}.  (Thanks to
      Martin Smith's report and suggestions in \PR{18109}.)

      \item \code{.First} and \code{.Last} can again be set from the site
      profile.

      \item \code{seq.int(from, to, *)} and \code{seq.default(..)} now work
      better in large range cases where \code{from-to} is infinite where
      the two boundaries are finite.

      \item \code{all.equal(x,y)} now returns \code{TRUE} correctly also
      when several entries of \code{abs(x)} and \code{abs(y)} are close to
      \code{.Machine$double.xmax}, the largest finite \code{numeric}.

      \item \code{model.frame()} now clears the object bit when removing the
      \code{class} attribute of a value via \code{na.action} (\PR{18100}).

      \item \code{charClass()} now works with multi-character
      strings on Windows (\PR{18104}, fixed by Bill Dunlap).

      \item \code{encodeString()} on Solaris now works again in Latin-1
      encoding on characters represented differently in UTF-8.  Support for
      surrogate pairs on Solaris has been improved.

      \item \code{file.show()} on Windows now works with non-ASCII path
      names representable in the current native encoding (\PR{18132}).

      \item Embedded \R on Windows can now find \R home directory via the
      registry even when installed only for the current user (\PR{18135}).

      \item \code{pretty(x)} with finite \code{x} now returns finite values
      also in the case where the extreme \code{x} values are close in size
      to the maximal representable number \code{.Machine$double.xmax}.

      Also, it's been tweaked for very small ranges and when a boundary is
      close (or equal) to zero; e.g., \code{pretty(c(0,1e-317))} no longer
      has negative numbers, currently still warning about a very small
      range, and \code{pretty(2^-(1024 - 2^-1/(c(24,10))))} is more accurate.

      \item The error message for not finding vignette files when weaving
      has correct file sizes now. (Thanks to Sebastian Meyer's \PR{18154}.)

      \item \code{dnbinom(20, <large>, 1)} now correctly gives 0, and
      similar cases are more accurate with underflow precaution.
      (Reported by Francisco Vera Alcivar in \PR{18072}.)
    }
  }
}


\section{\Rlogo CHANGES IN R 4.1.0}{
  \subsection{FUTURE DIRECTIONS}{
    \itemize{
      \item It is planned that the 4.1.x series will be the last to
      support 32-bit Windows, with production of binary packages for
      that series continuing until early 2023.
    }
  }

  \subsection{SIGNIFICANT USER-VISIBLE CHANGES}{
    \itemize{
      \item Data set \code{esoph} in package \pkg{datasets} now provides
      the correct numbers of controls; previously it had the numbers of
      cases added to these.  (Reported by Alexander Fowler in \PR{17964}.)
    }
  }

  \subsection{NEW FEATURES}{
    \itemize{
      \item \samp{www.omegahat.net} is no longer one of the repositories
      known by default to \code{setRepositories()}.  (Nowadays it only
      provides source packages and is often unavailable.)
      %% it had one Windows binary package for 4.0, none for 3.6.

      \item Function \code{package_dependencies()} (in package
      \pkg{tools}) can now use different dependency types for direct and
      recursive dependencies.

      \item The checking of the size of tarball in
      \command{R CMD check --as-cran <pkg>} may be tweaked via the new
      environment variable
      \env{_R_CHECK_CRAN_INCOMING_TARBALL_THRESHOLD_}, as suggested in
      \PR{17777} by Jan Gorecki.

      \item Using \code{c()} to combine a factor with other factors now
      gives a factor, an ordered factor when combining ordered factors
      with identical levels.

      \item \code{apply()} gains a \code{simplify} argument to allow
      disabling of simplification of results.

      \item The \code{format()} method for class \code{"ftable"} gets a
      new option \code{justify}.  (Suggested by Thomas Soeiro.)

      \item New \code{...names()} utility.  (Proposed by Neal Fultz in
      \PR{17705}.)

      \item \code{type.convert()} now warns when its \code{as.is} argument
      is not specified, as the help file always said it \emph{should}.  In
      that case, the default is changed to \code{TRUE} in line with its
      change in \code{read.table()} (related to \code{stringsAsFactors}) in
      \R 4.0.0.

      \item When printing list arrays, classed objects are now shown
      \emph{via} their \code{format()} value if this is a short enough
      character string, or by giving the first elements of their class
      vector and their length.

      \item \code{capabilities()} gets new entry \code{"Rprof"} which is
      \code{TRUE} when \R has been configured with the equivalent of
      \command{--enable-R-profiling} (as it is by default).  (Related to
      Michael Orlitzky's report \PR{17836}.)

      \item \code{str(xS4)} now also shows extraneous attributes of an
      S4 object \code{xS4}.

      \item Rudimentary support for vi-style tags in \code{rtags()} and
      \code{R CMD rtags} has been added.  (Based on a patch from Neal
      Fultz in \PR{17214}.)

      \item \code{checkRdContents()} is now exported from \pkg{tools}; it
      and also \code{checkDocFiles()} have a new option \code{chkInternal}
      allowing to check Rd files marked with keyword \code{"internal"} as
      well.  The latter can be activated for \command{R CMD check} via
      environment variable \env{_R_CHECK_RD_INTERNAL_TOO_}.

      \item New functions \code{numToBits()} and \code{numToInts()}
      extend the \code{raw} conversion utilities to (double precision)
      \code{numeric}.

      \item Functions \code{URLencode()} and \code{URLdecode()} in
      package \pkg{utils} now work on vectors of URIs.
      (Based on patch from Bob Rudis submitted with \PR{17873}.)

      \item \code{path.expand()} can expand \samp{~user} on most
      Unix-alikes even when \code{readline} is not in use.  It tries
      harder to expand \samp{~}, for example should environment variable
      \env{HOME} be unset.

      \item For HTML help (both dynamic and static), Rd file links to
      help pages in external packages are now treated as references to
      topics rather than file names, and fall back to a file link only
      if the topic is not found in the target package. The earlier rule
      which prioritized file names over topics can be restored by
      setting the environment variable \env{_R_HELP_LINKS_TO_TOPICS_} to
      a false value.

      \item \code{c()} now removes \code{NULL} arguments before
      dispatching to methods, thus simplifying the implementation of
      \code{c()} methods, \emph{but} for back compatibility keeps
      \code{NULL} when it is the first argument.  (From a report and
      patch proposal by Lionel Henry in \PR{17900}.)

      \item \code{Vectorize()}'s result function's environment no longer
      keeps unneeded objects.

      \item Function \code{...elt()} now propagates visibility
      consistently with \code{..n}.  (Thanks to Lionel Henry's
      \PR{17905}.)

      \item \code{capture.output()} no longer uses non-standard
      evaluation to evaluate its arguments.  This makes evaluation of
      functions like \code{parent.frame()} more consistent.  (Thanks to
      Lionel Henry's \PR{17907}.)

      \item \code{packBits(bits, type="double")} now works as inverse of
      \code{numToBits()}.  (Thanks to Bill Dunlap's proposal in
      \PR{17914}.)

      \item \code{curlGetHeaders()} has two new arguments,
      \code{timeout} to specify the timeout for that call (overriding
      \code{getOption("timeout")}) and \code{TLS} to specify the minimum
      TLS protocol version to be used for \code{https://} URIs
      (\emph{inter alia} providing a means to check for sites using
      deprecated TLS versions 1.0 and 1.1).

      \item For \code{nls()}, an optional constant \code{scaleOffset}
      may be added to the denominator of the relative offset convergence
      test for cases where the fit of a model is expected to be exact,
      thanks to a proposal by John Nash.  \code{nls(*, trace=TRUE)} now
      also shows the convergence criterion.

      \item Numeric differentiation \emph{via} \code{numericDeriv()}
      gets new optional arguments \code{eps} and \code{central}, the
      latter for taking central divided differences.  The latter can be
      activated for \code{nls()} via \code{nls.control(nDcentral =
      TRUE)}.

      \item \code{nls()} now passes the \code{trace} and \code{control}
      arguments to \code{getInitial()}, notably for all self-starting models,
      so these can also be fit in zero-noise situations via a
      \code{scaleOffset}.  For this reason, the \code{initial} function of a
      \code{selfStart} model must now have \code{...} in its argument list.

      \item \code{bquote(splice = TRUE)} can now splice expression
      vectors with attributes: this makes it possible to splice the
      result of \code{parse(keep.source = TRUE)}.  (Report and patch
      provided by Lionel Henry in \PR{17869}.)

      \item \code{textConnection()} gets an optional \code{name} argument.

      \item \code{get()}, \code{exists()}, and \code{get0()} now signal
      an error if the first argument has length greater than 1.
      Previously additional elements were silently ignored.  (Suggested
      by Antoine Fabri on R-devel.)

      \item \R{} now provides a shorthand notation for creating functions,
      e.g. \code{\(x) x + 1} is parsed as \code{function(x) x + 1}.

      \item \R{} now provides a simple native forward pipe syntax
      \code{|>}.  The simple form of the forward pipe inserts the
      left-hand side as the first argument in the right-hand side call.
      The pipe implementation as a syntax transformation was motivated
      by suggestions from Jim Hester and Lionel Henry.

      \item \code{all.equal(f, g)} for \code{function}s now by default also
      compares their \code{environment(.)}s, notably via new
      \code{all.equal} method for class \code{function}.  Comparison of
      \code{nls()} fits, e.g., may now need \code{all.equal(m1, m2,
	check.environment = FALSE)}.

      \item \code{.libPaths()} gets a new option \code{include.site},
      allowing to \emph{not} include the site library.  (Thanks to Dario
      Strbenac's suggestion and Gabe Becker's \PR{18016}.)

      \item Lithuanian translations are now available.  (Thanks to
      Rimantas Žakauskas.)

      \item \code{names()} now works for \code{DOTSXP} objects.  On the
      other hand, in \file{R-lang}, the R language manual, we now warn
      against relying on the structure or even existence of such
      dot-dot-dot objects.

      \item \code{all.equal()} no longer gives an error on \code{DOTSXP}
      objects.

      %% The Homebrew arm64 libs have cairo but not cairo-xlib
      \item \code{capabilities("cairo")} now applies only to the
      file-based devices as it is now possible (if very unusual) to
      build \R with Cairo support for those but not for \code{X11()}.

      \item There is optional support for tracing the progress of
      \code{loadNamespace()} --- see its help.

      \item (Not Windows.)
      \code{l10n_info()} reports an additional element, the name of the
      encoding as reported by the OS (which may differ from the
      encoding part (if any) of the result from
      \code{Sys.getlocale("LC_CTYPE")}.

      \item New function \code{gregexec()} which generalizes \code{regexec()}
      to find \emph{all} disjoint matches and all substrings
      corresponding to parenthesized subexpressions of the given regular
      expression.  (Contributed by Brodie Gaslam.)

      \item New function \code{charClass()} in package \pkg{utils} to
      query the wide-character classification functions in use (such as
      \code{iswprint}).

      \item The names of \code{quantile()}'s result no longer depend on the
      global \code{getOption("digits")}, but \code{quantile()} gets a new
      optional argument \code{digits = 7} instead.

      \item \code{grep()}, \code{sub()}, \code{regexp} and variants work
      considerably faster for long factors with few levels.  (Thanks to
      Michael Chirico's \PR{18063}.)

      \item Provide grouping of \code{x11()} graphics windows within
      a window manager such as \code{Gnome} or \code{Unity}; thanks to a
      patch by Ivan Krylov posted to R-devel.

      \item The \code{split()} method for class \code{data.frame} now
      allows the \code{f} argument to be specified as a formula.

      \item \code{sprintf} now warns on arguments unused by the format
      string.

      \item New palettes \code{"Rocket"} and \code{"Mako"} for
      \code{hcl.colors()} (approximating palettes of the same name
      from the \pkg{viridisLite} package).

      Contributed by Achim Zeileis.

      \item The base environment and its namespace are now locked (so
      one can no longer add bindings to these or remove from these).

      \item \command{Rterm} handling of multi-byte characters has been
      improved, allowing use of such characters when supported by the
      current locale.

      \item \command{Rterm} now accepts \code{ALT+ +xxxxxxxx} sequences to
      enter Unicode characters as hex digits.

      \item Environment variable \env{LC_ALL} on Windows now takes
      precedence over \env{LC_CTYPE} and variables for other supported
      categories, matching the POSIX behaviour.

      \item \code{duplicated()} and \code{anyDuplicated()} are now
      optimized for integer and real vectors that are known to be sorted
      via the ALTREP framework. Contributed by Gabriel Becker via \PR{17993}.
    }
  }

  \subsection{GRAPHICS}{
    \itemize{
      \item The graphics engine version, \code{R_GE_version}, has been
      bumped to \code{14} and so packages that provide graphics devices
      should be reinstalled.

      \item Graphics devices should now specify \code{deviceVersion} to
      indicate what version of the graphics engine they support.

      \item Graphics devices can now specify \code{deviceClip}.  If
      \code{TRUE}, the graphics engine will never perform any clipping
      of output itself.

      The clipping that the graphics engine does perform (for both
      \code{canClip = TRUE} and \code{canClip = FALSE}) has been
      improved to avoid producing unnecessary artifacts in clipped
      output.

      \item The \pkg{grid} package now allows \code{gpar(fill)} to be
      a \code{linearGradient()}, a \code{radialGradient()}, or a
      \code{pattern()}.  The \code{viewport(clip)} can now also be
      a grob, which defines a clipping path, and there is a new
      \code{viewport(mask)} that can also be a grob, which defines
      a mask.

      These new features are only supported so far on the Cairo-based
      graphics devices and on the \code{pdf()} device.

      \item (Not Windows.)
      A warning is given when a Cairo-based type is specified for a
      \code{png()}, \code{jpeg()}, \code{tiff()} or \code{bmp()}
      device but Cairo is unsupported (so \code{type = "Xlib"}
      is tried instead).

      \item \code{grSoftVersion()} now reports the versions of FreeType
      and FontConfig if they are used directly (not \emph{via} Pango),
      as is most commonly done on macOS.
    }
  }

  \subsection{C-LEVEL FACILITIES}{
    \itemize{
      \item The \emph{standalone} \file{libRmath} math library and \R's C
      API now provide \code{log1pexp()} again as documented, and gain
      \code{log1mexp()}.
    }
  }

  \subsection{INSTALLATION on a UNIX-ALIKE}{
    \itemize{
      \item \command{configure} checks for a program \command{pkgconf}
      if program \command{pkg-config} is not found.  These are now only
      looked for on the path (like almost all other programs) so if needed
      specify a full path to the command in \code{PKG_CONFIG}, for example
      in file \file{config.site}.

      \item C99 function \code{iswblank} is required -- it was last seen
      missing ca 2003 so the workaround has been removed.

      \item There are new \command{configure} options
      \option{--with-internal-iswxxxxx},
      \option{--with-internal-towlower} and
      \option{--with-internal-wcwidth} which allows the system functions
      for wide-character classification, case-switching and width
      (\code{wcwidth} and \code{wcswidth}) to be replaced by internal
      ones.  The first has long been used on macOS, AIX (and Windows)
      but this enables it to be unselected there and selected for other
      platforms (it is the new default on Solaris).  The second is new
      in this version of \R and is selected by default on macOS and
      Solaris.  The third has long been the default and remains so as it
      contains customizations for East Asian languages.

      System versions of these functions are often minimally implemented
      (sometimes only for ASCII characters) and may not cover the full
      range of Unicode points: for example Solaris (and Windows) only
      cover the Basic Multilingual Plane.

      \item Cairo installations without X11 are more likely to be
      detected by \command{configure}, when the file-based Cairo
      graphics devices will be available but not \code{X11(type =
      "cairo")}.

      \item There is a new \command{configure} option
      \option{--with-static-cairo} which is the default on macOS.  This
      should be used when only static cairo (and where relevant, Pango)
      libraries are available.

      \item Cairo-based graphics devices on platforms without Pango but
      with FreeType/FontConfig will make use of the latter for font selection.
    }
  }


  \subsection{LINK-TIME OPTIMIZATION on a UNIX-ALIKE}{
    \itemize{
      \item Configuring with flag \option{--enable-lto=R} now also uses
      LTO when installing the recommended packages.

      \item \command{R CMD INSTALL} and \command{R CMD SHLIB} have a new
      flag \option{--use-LTO} to use LTO when compiling code, for use
      with \R configured with \option{--enable-lto=R}.  For \R
      configured with \option{--enable-lto}, they have the new flag
      \option{--no-use-LTO}.

      Packages can opt in or out of LTO compilation \emph{via} a
      \samp{UseLTO} field in the \file{DESCRIPTION} file.  (As usual this
      can be overridden by the command-line flags.)
    }
  }

  \subsection{BUILDING R on Windows}{
    \itemize{
      \item for GCC \eqn{\ge}{>=} 8, \code{FC_LEN_T} is defined in
      \file{config.h} and hence character lengths are passed from C to
      Fortran in \emph{inter alia} BLAS and LAPACK calls.

      \item There is a new text file
      \file{src/gnuwin32/README.compilation}, which outlines how C/Fortran
      code compilation is organized and documents new features:
      \itemize{
	\item \R can be built with Link-Time Optimization with a
	suitable compiler -- doing so with GCC 9.2 showed several
	inconsistencies which have been corrected.

	\item There is support for cross-compiling the C and Fortran
	code in \R and standard packages on suitable (Linux) platforms.
	This is mainly intended to allow developers to test later
	versions of compilers -- for example using GCC 9.2 or 10.x has
	detected issues that GCC 8.3 in Rtools40 does not.

	\item There is experimental support for cross-building \R
	packages with C, C++ and/or Fortran code.
      }

      \item The R installer can now be optionally built to support a single
      architecture (only 64-bit or only 32-bit).
    }
  }

  \subsection{PACKAGE INSTALLATION}{
    \itemize{
      \item The default C++ standard has been changed to C++14 where
      available (which it is on all currently checked platforms): if not
      (as before) C++11 is used if available otherwise C++ is not
      supported.

      Packages which specify C++11 will still be installed using C++11.

      C++14 compilers may give deprecation warnings, most often for
      \code{std::random_shuffle} (deprecated in C++14 and removed in
      C++17).  Either specify C++11 (see \sQuote{Writing R Extensions})
      or modernize the code and if needed specify C++14.  The latter has
      been supported since \R 3.4.0 so the package's \file{DESCRIPTION}
      would need to include something like
\preformatted{
     Depends: R (>= 3.4)
}
    }
  }

  \subsection{PACKAGE INSTALLATION on Windows}{
    \itemize{
      \item \command{R CMD INSTALL} and \command{R CMD SHLIB} make use
      of their flag \option{--use-LTO} when the \samp{LTO_OPT} make
      macro is set in file \file{etc/$\{R_ARCH\}/Makeconf} or in a
      personal/site \file{Makevars} file.  (For details see
      \sQuote{Writing R Extensions} §4.5.)

      This provides a valuable check on code consistency.  It does work
      with GCC 8.3 as in Rtools40, but that does not detect everything
      the \acronym{CRAN} checks with current GCC do.
    }
  }

  \subsection{PACKAGE INSTALLATION on macOS}{
    \itemize{
      \item The default personal library directory on builds with
      \option{--enable-aqua} (including \acronym{CRAN} builds) now
      differs by CPU type, one of
\preformatted{
      ~/Library/R/x86_64/x.y/library
      ~/Library/R/arm64/x.y/library
}
      This uses the CPU type \R (and hence the packages) were built for,
      so when a \samp{x86_64} build of R is run under Rosetta emulation on
      an \samp{arm64} Mac, the first is used.
    }
  }

  \subsection{UTILITIES}{
    \itemize{
      \item \command{R CMD check} can now scan package functions for
      bogus \code{return} statements, which were possibly intended as
      \code{return()} calls (wish of \PR{17180}, patch by Sebastian
      Meyer). This check can be activated via the new environment
      variable \env{_R_CHECK_BOGUS_RETURN_}, true for \code{--as-cran}.

      \item \command{R CMD build} omits tarballs and binaries of
      previous builds from the top-level package directory.
      (\PR{17828}, patch by Sebastian Meyer.)

      \item \command{R CMD check} now runs sanity checks on the use of
      \samp{LazyData}, for example that a \file{data} directory is
      present and that \samp{LazyDataCompression} is not specified
      without \samp{LazyData} and has a documented value.  For packages
      with large LazyData databases without specifying
      \samp{LazyDataCompression}, there is a reference to the code given
      in \sQuote{Writing R Extensions} §1.1.6 to test the choice of
      compression (as in all the \acronym{CRAN} packages tested a
      non-default method was preferred).

      \item \command{R CMD build} removes \samp{LazyData} and
      \samp{LazyDataCompression} fields from the \file{DESCRIPTION} file
      of packages without a \file{data} directory.
    }
  }

  \subsection{ENCODING-RELATED CHANGES}{
    \itemize{
      \item The parser now treats \samp{\\Unnnnnnnn} escapes larger than
      the upper limit for Unicode points (\samp{\\U10FFFF}) as an error
      as they cannot be represented by valid UTF-8.

      Where such escapes are used for outputting non-printable
      (including unassigned) characters, 6 hex digits are used (rather
      than 8 with leading zeros).  For clarity, braces are used, for
      example \samp{\\U\{0effff\}}.

      \item The parser now looks for non-ASCII spaces on Solaris (as
      previously on most other OSes).

      \item There are warnings (including from the parser) on the use of
      unpaired surrogate Unicode points such as \samp{\\uD834}.  (These
      cannot be converted to valid UTF-8.)

      \item Functions \code{nchar()}, \code{tolower()}, \code{toupper()}
      and \code{chartr()} and those using regular expressions have more
      support for inputs with a marked Latin-1 encoding.

      \item The character-classification functions used (by default) to
      replace the system \code{iswxxxxx} functions on Windows, macOS and
      AIX have been updated to Unicode 13.0.0.

      The character-width tables have been updated to include new
      assignments in Unicode 13.0.0.  This included treating all control
      characters as having zero width.

      \item The code for evaluating default (extended) regular
      expressions now uses the same character-classification functions
      as the rest of \R (previously they differed on Windows, macOS and
      AIX).

      \item There is a build-time option to replace the system's
      wide-character \code{wctrans} C function by tables shipped with
      \R: use \command{configure} option
      \option{--with-internal-towlower} or (on Windows)
      \samp{-DUSE_RI18N_CASE} in \samp{CFLAGS} when building \R.  This
      may be needed to allow \code{tolower()} and \code{toupper()} to
      work with Unicode characters beyond the Basic Multilingual Plane
      where not supported by system functions (e.g. on Solaris where it
      is the new default).

      \item R is more careful when truncating UTF-8 and other multi-byte
      strings that are too long to be printed, passed to the system or
      libraries or placed into an internal buffer.  Truncation will no
      longer produce incomplete multibyte characters.
    }
  }

  \subsection{DEPRECATED AND DEFUNCT}{
    \itemize{
      \item Function \code{plclust()} from the package \pkg{stats} and
      \code{package.dependencies()}, \code{pkgDepends()},
      \code{getDepList()}, \code{installFoundDepends()}, and
      \code{vignetteDepends()} from package \pkg{tools} are defunct.

      \item Defunct functions \code{checkNEWS()} and \code{readNEWS()} from
      package \pkg{tools} and \code{CRAN.packages()} from \pkg{utils} have
      been removed.

      \item \command{R CMD config CXXCPP} is defunct (it was deprecated
      in \R{} 3.6.2).

      \item \code{parallel::detectCores()} drops support for Irix
      (retired in 2013).

      \item The \code{LINPACK} argument to \code{chol.default()},
      \code{chol2inv()}, \code{solve.default()} and \code{svd()} has
      been defunct since \R 3.1.0.  It was silently ignored up to \R
      4.0.3 but now gives an error.

      \item Subsetting/indexing, such as \code{ddd[*]} or \code{ddd$x}
      on a \code{DOTSXP} (dot-dot-dot) object \code{ddd} has been
      disabled; it worked by accident only and was undocumented.
    }
  }

  \subsection{BUG FIXES}{
    \itemize{
      \item Many more C-level allocations (mainly by \code{malloc} and
      \code{strdup}) are checked for success with suitable alternative
      actions.

      \item Bug fix for \code{replayPlot()};  this was turning off
      graphics engine display list recording if a recorded plot was
      replayed in the same session.  The impact of the bug became
      visible if resize the device after replay OR if attempted another
      \code{savePlot()} after replay (empty display list means empty
      screen on resize or empty saved plot).

      \item \command{R CMD check} etc now warn when a package exports
      non-existing S4 classes or methods, also in case of no
      \dQuote{methods} presence.  (Reported by Alex Bertram;
      reproducible example and patch by Sebastian Meyer in \PR{16662}.)

      \item \code{boxplot()} now also accepts \code{call}s for labels such
      as \code{ylab}, the same as \code{plot()}.  (Reported by Marius Hofert.)

      \item The help page for \code{xtabs()} now correctly states that
      \code{addNA} is setting \code{na.action = na.pass} among others.
      (Reported as \PR{17770} by Thomas Soeiro.)

      \item The \command{R CMD check <pkg>} gives a longer and more
      comprehensible message when \file{DESCRIPTION} misses dependencies,
      e.g., in \code{Imports:}.  (Thanks to the contributors of \PR{17179}.)

      \item \code{update.default()} now calls the generic \code{update()}
      on the formula to work correctly for models with extended formulas.
      (As reported and suggested by Neal Fultz in \PR{17865}.)

      \item The horizontal position of leaves in a dendrogram is now
      correct also with \code{center = FALSE}.  (\PR{14938}, patch from
      Sebastian Meyer.)

      \item \code{all.equal.POSIXt()} no longer warns about and
      subsequently ignores inconsistent \code{"tzone"} attributes, but
      describes the difference in its return value (\PR{17277}).
      This check can be disabled \emph{via} the new argument
      \code{check.tzone = FALSE} as suggested by Sebastian Meyer.

      \item \code{as.POSIXct()} now populates the \code{"tzone"}
      attribute from its \code{tz} argument when \code{x} is a logical
      vector consisting entirely of \code{NA} values.

      \item \code{x[[2^31]] <- v} now works.  (Thanks to the report and
      patch by Suharto Anggono in \PR{17330}.)

      \item In log-scale graphics, \code{axis()} ticks and label positions
      are now computed more carefully and symmetrically in their range,
      typically providing \emph{more} ticks, fulfilling wishes
      in \PR{17936}.  The change really corresponds to an improved
      \code{axisTicks()} (package \pkg{grDevices}), potentially influencing
      \pkg{grid} and \pkg{lattice}, for example.

      \item \code{qnorm(<very large negative>, log.p=TRUE)} is now correct
      to at least five digits where it was catastrophically wrong,
      previously.

      \item \code{sum(df)} and similar \code{"Summary"}- and
      \code{"Math"}-group member functions now work for data frames
      \code{df} with \code{\link{logical}} columns, notably also of zero
      rows.  (Reported to R-devel by Martin \dQuote{b706}.)

      \item \code{unsplit()} had trouble with tibbles due to unsound use of
      \code{rep(NA, len)}-indexing, which should use \code{NA_integer_}
      (Reported to R-devel by Mario Annau.)

      \item \code{pnorm(x, log.p = TRUE)} underflows to \code{-Inf} slightly
      later.

      \item \code{show(<hidden S4 generic>)} prints better and without
      quotes for non-hidden S4 generics.

      \item \code{read.table()} and relatives treated an "NA" column name as
      missing when \code{check.names = FALSE} \PR{18007}.

      \item Parsing strings containing UTF-16 surrogate pairs such as
      \code{"\uD834\uDD1E"} works better on some (uncommon) platforms.
      \code{sprintf("\%X", utf8ToInt("\uD834\uDD1E"))} should now give
      \code{"1D11E"} on all platforms.
      %% failed on Solaris

      \item \code{identical(x,y)} is no longer true for differing
      \code{DOTSXP} objects, fixing \PR{18032}.

      \item \code{str()} now works correctly for \code{DOTSXP} and related
      exotics, even when these are doomed.

      Additionally, it no longer fails for \code{list}s with a \code{class} and
      \dQuote{irregular} method definitions such that e.g. \code{lapply(*)} will
      necessarily fail, as currently for different \CRANpkg{igraph} objects.

      \item Message translation domains, e.g., for errors and warnings, are
      now correctly determined also when e.g., a \pkg{base} function is
      called from \dQuote{top-level} function (i.e., defined in \code{globalenv()}),
      thanks to a patch from Joris Goosen fixing \PR{17998}.

      \item Too long lines in environment files (e.g., \file{Renviron}) no
      longer crash \R. This limit has been increased to 100,000 bytes.
      (\PR{18001}.)

      \item There is a further workaround for FreeType giving
      incorrect italic font faces with cairo-based graphics devices on
      macOS.

      \item \code{add_datalist(*, force = TRUE)} (from package
      \pkg{tools}) now actually updates an existing \file{data/datalist}
      file for new content.  (Thanks to a report and patch by Sebastian
      Meyer in \PR{18048}.)

      \item \code{cut.Date()} and \code{cut.POSIXt()} could produce an
      empty last interval for \code{breaks = "months"} or \code{breaks =
      "years"}.  (Reported as \PR{18053} by Christopher Carbone.)

      \item Detection of the encoding of \sQuote{regular} macOS locales
      such as \samp{en_US} (which is UTF-8) had been broken by a macOS
      change: fortunately these are now rarely used with
      \samp{en_US.UTF-8} being preferred.

      \item \code{sub()} and \code{gsub(pattern, repl, x, *)} now keep
      attributes of \code{x} such as \code{names()} also when
      \code{pattern} is \code{NA} (\PR{18079}).

      \item Time differences (\code{"difftime"} objects) get a replacement
      and a \code{rep()} method to keep \code{"units"} consistent.
      (Thanks to a report and patch by Nicolas Bennett in \PR{18066}.)

      \item The \verb{\RdOpts} macro, setting defaults for \verb{\Sexpr}
      options in an Rd file, had been ineffective since \R 2.12.0: it
      now works again.
      (Thanks to a report and patch by Sebastian Meyer in \PR{18073}.)

      \item \code{mclapply} and \code{pvec} no longer accidentally terminate
      parallel processes started before by \code{mcparallel} or related
      calls in package \pkg{parallel} (\PR{18078}).

      \item \code{grep} and other functions for evaluating (extended)
      regular expressions handle in Unicode also strings not explicitly
      flagged UTF-8, but flagged native when running in UTF-8 locale.

      \item Fixed a crash in \code{fifo} implementation on Windows
      (\PR{18031}).

      \item Binary mode in \code{fifo} on Windows is now properly detected
      from argument \code{open} (\PR{15600}, \PR{18031}).
    }
  }
}

\section{\Rlogo CHANGES IN R 4.0.5}{
  \subsection{BUG FIXES}{
    \itemize{
      \item The change to the internal table in \R 4.0.4 for
      \code{iswprint} has been reverted: it contained some errors in
      printability of \sQuote{East Asian} characters.

      \item For packages using \samp{LazyData}, \command{R CMD build}
      ignored the \option{--resave-data} option and the
      \samp{BuildResaveData} field of the \file{DESCRIPTION} file (in \R
      versions 4.0.0 to 4.0.4).
    }
  }
}

\section{\Rlogo CHANGES IN R 4.0.4}{

  \subsection{NEW FEATURES}{
    \itemize{
      \item File \file{share/texmf/tex/latex/jss.cls} has been updated
      to work with LaTeX versions since Oct 2020.

      \item Unicode character width tables (as used by
      \code{nchar(, type = "w")}) have been updated to Unicode 12.1
      by Brodie Gaslam (\PR{17781}), including many emoji.

      \item The internal table for \code{iswprint} (used on Windows,
      macOS and AIX) has been updated to include many recent Unicode
      characters.
    }
  }

  \subsection{INSTALLATION on a UNIX-ALIKE}{
    \itemize{
      \item If an external BLAS is specified by \option{--with-blas=foo}
      or \emph{via} environment variable \env{BLAS_LIBS} is not found,
      this is now a configuration error.  The previous behaviour was not
      clear from the documentation: it was to continue the search as if
      \option{--with-blas=yes} was specified.
    }
  }

  \subsection{BUG FIXES}{
    \itemize{
      \item \code{all.equal(x,y)} now \dQuote{sees} the two different
      \code{NA}s in factors, thanks to Bill Dunlap and others in
      \PR{17897}.

      \item \code{(~ NULL)[1]} and similar formula subsetting now works,
      thanks to a report and patch by Henrik Bengtsson in \PR{17935}.
      Additionally, subsetting leaving an empty formula now works too,
      thanks to suggestions by Suharto Anggono.

      \item \code{.traceback(n)} keeps source references again, as before
      \R 4.0.0, fixing a regression; introduced by the \PR{17580}, reported
      including two patch proposals by Brodie Gaslam.

      \item \code{unlist(plst, recursive=FALSE)} no longer drops content
      for pairlists with list components, thanks to the report and patch
      by Suharto Anggono in \PR{17950}.

      \item \code{iconvlist()} now also works on MUSL based (Linux)
      systems, from a report and patch suggestion by Wesley Chan in
      \PR{17970}.

      \item \code{round()} and \code{signif()} no longer tolerate wrong
      argument names, notably in 1-argument calls; reported by Shane
      Mueller on R-devel (mailing list); later reported as \PR{17976}.

      \item \code{.Machine} has \code{longdouble.*} elements only if
      \code{capabilities("long.double")} is true, as documented.
      (Previously they were included if the platform had \code{long
	double} identical to \code{double}, as ARM does.)

      \item \code{p.adjust(numeric(), n=0)} now works, fixing \PR{18002}.

      \item \code{identical(x,y)} no longer prints "Unknown Type .." for
      \code{typeof(x) == "..."} objects.

      \item Fix (auto-)\code{print()}ing of named complex vectors, see
      \PR{17868} and \PR{18019}.

      \item \code{all.equal(<language>, <...>)} now works, fixing \PR{18029}.

      \item \code{as.data.frame.list(L, row.names=NULL)} now behaves in line
      with \code{data.frame()}, disregarding names of components of
      \code{L}, fixing \PR{18034}, reported by Kevin Tappe.

      \item \code{checkRdaFiles(ff)$version} is now correct also when
      \code{ff} contains files of different versions, thanks to a report
      and patch from Sebastian Meyer in \PR{18041}.

      \item macOS: Quartz device live drawing could fail (no plot is shown)
      if the system changes the drawing context after view update (often
      the case since macOS Big Sur). System log may show
      "CGContextDelegateCreateForContext: invalid context" error.
    }
  }
}

\section{\Rlogo CHANGES IN R 4.0.3}{

  \subsection{NEW FEATURES}{
    \itemize{
      \item On platforms using \command{configure} option
      \option{--with-internal-tzcode}, additional values
      \code{"internal"} and (on macOS only) \code{"macOS"} are accepted
      for the environment variable \env{TZDIR}.  (See \code{?TZDIR}.)

      On macOS, \code{"macOS"} is used by default if the system timezone
      database is a newer version than that in the \R installation.

      \item When \code{install.packages(type = "source")} fails to find
       a package in a repository it mentions package versions which are
       excluded by their \R version requirement and links to hints on
       why a package might not be found.

       \item The default value for \code{options("timeout")} can be set
       from environment variable \env{R_DEFAULT_INTERNET_TIMEOUT}, still
       defaulting to 60 (seconds) if that is not set or invalid.

       This may be needed when child \R processes are doing downloads,
       for example during the installation of source packages which
       download jars or other forms of data.
     }
  }

  \subsection{LINK-TIME OPTIMIZATION on a UNIX-ALIKE}{
    \itemize{
      \item There is now support for parallelized Link-Time Optimization
      (LTO) with GCC and for \sQuote{thin} LTO with
      \command{clang} \emph{via} setting the \samp{LTO} macro.

      \item There is support for setting a different LTO flag for the
      Fortran compiler, including to empty when mixing \command{clang}
      and \command{gfortran} (as on macOS).  See file \file{config.site}.

      \item There is a new \samp{LTO_LD} macro to set linker options for
      LTO compilation, for example to select an alternative linker or
      to parallelize thin LTO.
    }
  }

    \subsection{DEPRECATED AND DEFUNCT}{
    \itemize{

      \item The \code{LINPACK} argument to \code{chol.default()},
      \code{chol2inv()}, \code{solve.default()} and \code{svd()} has been
      defunct since \R 3.1.0.  Using it now gives a warning which will
      become an error in \R 4.1.0.
    }
  }

  \subsection{BUG FIXES}{
    \itemize{
      \item The code mitigating stack overflow with PCRE regexps on very
      long strings is enabled for PCRE2 < 10.30 also when JIT is enabled,
      since stack overflows have been seen in that case.
      %% Ubuntu 16.04LTS has PCRE2 10.21

      \item Fix to correctly show the group labels in \code{dotchart()}
      (which where lost in the \code{ylab} improvement for \R 4.0.0).

      \item \code{addmargins(*, ..)} now also works when \code{fn()} is a
      local function, thanks to bug report and patch \PR{17124} from Alex
      Bertram.

      \item \code{rank(x)} and hence \code{sort(x)} now work when \code{x}
      is an object (as per \code{is.object(x)}) of type \code{"raw"}
      \emph{and} provides a valid \code{`[`} method, e.g., for
      \code{gmp::as.bigz(.)} numbers.

      \item \code{chisq.test(*, simulate.p.value=TRUE)} and
      \code{r2dtable()} now work correctly for large table entries (in the
      millions).  Reported by Sebastian Meyer and investigated by more
      helpers in \PR{16184}.

      \item Low-level socket read/write operations have been fixed to
      correctly signal communication errors. Previously, such errors could
      lead to a segfault due to invalid memory access. Reported
      and debugged by Dmitriy Selivanov in \PR{17850}.

      \item \code{quantile(x, pr)} works more consistently for \code{pr}
      values slightly outside [0,1], thanks to Suharto Anggono's \PR{17891}.

      Further, \code{quantile(x, prN, names=FALSE)} now works even when
      \code{prN} contains \code{NA}s, thanks to Anggono's \PR{17892}.
      Ditto for ordered factors or \code{Date} objects
      when \code{type = 1} or \code{3}, thanks to \PR{17899}.

      \item Libcurl-based internet access, including
      \code{curlGetHeaders()}, was not respecting the \code{"timeout"}
      option.  If this causes unanticipated timeouts, consider
      increasing the default by setting \env{R_DEFAULT_INTERNET_TIMEOUT}.

      \item \code{as.Date(<char>)} now also works with an initial
      \code{""}, thanks to Michael Chirico's \PR{17909}.

      \item \code{isS3stdGeneric(f)} now detects an S3 generic also when it
      it is \code{trace()}d, thanks to Gabe Becker's \PR{17917}.

      \item \code{R_allocLD()} has been fixed to return memory aligned for
      long double type \PR{16534}.

      \item \code{fisher.test()} no longer segfaults when called again after
      its internal stack has been exceeded \PR{17904}.

      \item Accessing a long vector represented by a compact integer
      sequence no longer segfaults (reported and debugged by Hugh
      Parsonage).

      \item \code{duplicated()} now works also for strings with multiple
      encodings inside a single vector \PR{17809}.

      \item \code{phyper(11, 15, 0, 12, log.p=TRUE)} no longer gives
      \code{NaN}; reported as \PR{17271} by Alexey Stukalov.

      \item Fix incorrect calculation in \code{logLik.nls()} \PR{16100}, patch
      from Sebastian Meyer.

      \item A very old bug could cause a segfault in \code{model.matrix()}
      when terms involved logical variables.  Part of \PR{17879}.

      \item \code{model.frame.default()} allowed \code{data = 1}, leading to
      involuntary variable capture (rest of \PR{17879}).

      \item \code{tar()} no longer skips non-directory files, thanks to a
      patch by Sebastian Meyer, fixing the remaining part of \PR{16716}.
    }
  }
}


\section{\Rlogo CHANGES IN R 4.0.2}{

  \subsection{UTILITIES}{
    \itemize{
      \item \command{R CMD check} skips vignette re-building (with a
      warning) if the \samp{VignetteBuilder} package(s) are not available.
    }
  }

  \subsection{BUG FIXES}{
    \itemize{
      \item Paths with non-ASCII characters caused problems for
      package loading on Windows \PR{17833}.

      \item Using \pkg{tcltk} widgets no longer crashes R on
      Windows.

      \item \code{source(*, echo=TRUE)} no longer fails in some cases with
      empty lines; reported by Bill Dunlap in \PR{17769}.

      \item \code{on.exit()} now correctly matches named arguments, thanks
      to \PR{17815} (including patch) by Brodie Gaslam.

      \item \code{regexpr(*, perl=TRUE)} no longer returns incorrect
      positions into text containing characters outside of the Unicode
      Basic Multilingual Plane on Windows.
    }
  }
}

\section{\Rlogo CHANGES IN R 4.0.1}{

  \subsection{NEW FEATURES}{
    \itemize{
      \item \code{paste()} and \code{paste0()} gain a new optional
      argument \code{recycle0}.  When set to true, zero-length
      arguments are recycled leading to \code{character(0)} after the
      \code{sep}-concatenation, i.e., to the empty string \code{""} if
      \code{collapse} is a string and to the zero-length value
      \code{character(0)} when \code{collapse = NULL}.

      A package whose code uses this should depend on \samp{R (>= 4.0.1)}.

      \item The \code{summary(<warnings>)} method now maps the counts
      correctly to the warning messages.
    }
  }

  \subsection{BUG FIXES}{
    \itemize{
      \item \code{aov(frml, ...)} now also works where the \code{formula}
      deparses to more than 500 characters, thanks to a report and patch
      proposal by Jan Hauffa.

      \item Fix a dozen places (code, examples) as \code{Sys.setlocale()}
      returns the new rather than the previous setting.

      \item Fix for adding two complex \pkg{grid} units via \code{sum()}.
      Thanks to Gu Zuguang for the report and Thomas Lin Pedersen for
      the patch.

      \item Fix \code{parallel::mclapply(..., mc.preschedule=FALSE)}
      to handle raw vector results correctly. \PR{17779}

      \item Computing the \code{base} value, i.e., 2, \dQuote{everywhere},
      now uses \code{FLT_RADIX}, as the original \file{machar} code looped
      indefinitely on the ppc64 architecture for the \code{longdouble} case.

      \item In \R 4.0.0, \code{sort.list(x)} when \code{is.object(x)} was
      true, e.g., for \code{x <- I(letters)}, was accidentally using
      \code{method = "radix"}.  Consequently, e.g., \code{merge(<data.frame>)}
      was much slower than previously; reported in \PR{17794}.

      \item \code{plot(y ~ x, ylab = quote(y[i]))} now works, as e.g., for
      \code{xlab}; related to \PR{10525}.

      \item \code{parallel::detect.cores(all.tests = TRUE)} tries a
      matching OS name before the other tests (which were intended only
      for unknown OSes).

      \item Parse data for raw strings is now recorded correctly. Reported
      by Gabor Csardi.
    }
  }
}

\section{\Rlogo CHANGES IN R 4.0.0}{

  \subsection{SIGNIFICANT USER-VISIBLE CHANGES}{
    \itemize{
      \item Packages need to be (re-)installed under this version
      (4.0.0) of \R.

      \item \code{matrix} objects now also inherit from class
      \code{"array"}, so e.g., \code{class(diag(1))} is \code{c("matrix",
	"array")}.  This invalidates code incorrectly assuming that
      \code{class(matrix_obj))} has length one.

      S3 methods for class \code{"array"} are now dispatched for
      \code{matrix} objects.

      \item There is a new syntax for specifying \emph{raw} character
      constants similar to the one used in C++: \code{r"(...)"} with
      \code{...} any character sequence not containing the sequence
      \samp{)"}. %}) \samp{*}: Rd-parser bug for \code{*}"
      This makes it easier to write strings that contain backslashes or
      both single and double quotes.  For more details see \code{?Quotes}.

      \item \R now uses a \samp{stringsAsFactors = FALSE} default, and
      hence by default no longer converts strings to factors in calls
      to \code{data.frame()} and \code{read.table()}.

      A large number of packages relied on the previous behaviour and
      so have needed/will need updating.

      \item The \code{plot()} S3 generic function is now in package
      \pkg{base} rather than package \pkg{graphics}, as it is
      reasonable to have methods that do not use the \pkg{graphics}
      package.  The generic is currently re-exported from the
      \pkg{graphics} namespace to allow packages importing it from
      there to continue working, but this may change in future.

      Packages which define S4 generics for \code{plot()} should be
      re-installed and package code using such generics from other
      packages needs to ensure that they are imported rather than rely
      on their being looked for on the search path (as in a namespace,
      the base namespace has precedence over the search path).
    }
  }

  \subsection{REFERENCE COUNTING}{
    \itemize{
       \item Reference counting is now used instead of the \code{NAMED}
       mechanism for determining when objects can be safely mutated in
       base C code.  This reduces the need for copying in some cases and
       should allow further optimizations in the future.  It should
       help make the internal code easier to maintain.

       This change is expected to have almost no impact on packages
       using supported coding practices in their C/C++ code.
     }
   }

  \subsection{MIGRATION TO PCRE2}{
    \itemize{
       \item This version of \R is built against the PCRE2 library for
       Perl-like regular expressions, if available.  (On non-Windows
       platforms PCRE1 can optionally be used if PCRE2 is not available
       at build time.)  The version of PCRE in use can be obtained
       \emph{via} \code{extSoftVersion()}: PCRE1 (formerly known as
       \sQuote{PCRE}) has versions <= 8, PCRE2 versions >= 10.

       \item Making PCRE2 available when building \R from source is
       strongly recommended (preferably version 10.30 or later) as PCRE1
       is no longer developed: version 8.44 is
       \sQuote{likely to be the final release}.
       % https://lists.exim.org/lurker/message/20200212.174850.6edd8277.en.html

       \item PCRE2 reports errors for some regular expressions that were
       accepted by PCRE1.  A hyphen now has to be escaped in a character
       class to be interpreted as a literal (unless first or last in the
       class definition).  \samp{\\R}, \samp{\\B} and \samp{\\X} are no
       longer allowed in character classes (PCRE1 treated these as
       literals).

       \item Option \code{PCRE_study} is no longer used with PCRE2, and is
       reported as \code{FALSE} when that is in use.
     }
  }

  \subsection{NEW FEATURES}{
    \itemize{
      \item \code{assertError()} and \code{assertWarning()} (in package
      \pkg{tools}) can now check for \emph{specific} error or warning
      classes \emph{via} the new optional second argument \code{classes}
      (which is not back compatible with previous use of an unnamed second
      argument).

      \item \code{DF2formula()}, the utility for the data frame method of
      \code{formula()}, now works without parsing and explicit evaluation,
      starting from Suharto Anggono's suggestion in \PR{17555}.

      \item \code{approxfun()} and \code{approx()} gain a new argument
      \code{na.rm} defaulting to true.  If set to false, missing
      \code{y} values now propagate into the interpolated values.

      \item Long vectors are now supported as the \code{seq} argument of
      a \code{for()} loop.

      \item \code{str(x)} gets a new \code{deparse.lines} option with a
      default to speed it up when \code{x} is a large \code{call} object.

      \item The internal traceback object produced when an error is
      signalled (\code{.Traceback}), now contains the \code{call}s
      rather than the \emph{\code{deparse()}d} calls, deferring the
      deparsing to the user-level functions \code{.traceback()} and
      \code{traceback()}.  This fulfils the wish of \PR{17580}, reported
      including two patch proposals by Brodie Gaslam.

      \item \code{data.matrix()} now converts character columns to
      factors and from this to integers.

      \item \code{package.skeleton()} now explicitly lists all exports
      in the \file{NAMESPACE} file.

      \item New function \code{.S3method()} to register S3 methods in R
      scripts.

      \item \code{file.path()} has some support for file paths not in
      the session encoding, e.g.\sspace{}with UTF-8 inputs in a
      non-UTF-8 locale the output is marked as UTF-8.

      \item Most functions with file-path inputs will give an explicit
      error if a file-path input in a marked encoding cannot be
      translated (to the native encoding or in some cases on Windows to
      UTF-8), rather than translate to a different file path using
      escapes.  Some (such as \code{dir.exists()}, \code{file.exists()},
      \code{file.access()}, \code{file.info()}, \code{list.files()},
      \code{normalizePath()} and \code{path.expand()}) treat this like
      any other non-existent file, often with a warning.

      \item There is a new help document accessed by
      \code{help("file path encoding")} detailing how file paths with
      marked encodings are handled.

      \item New function \code{list2DF()} for creating data frames from
      lists of variables.

      \item \code{iconv()} has a new option \code{sub = "Unicode"} to
      translate UTF-8 input invalid in the \samp{to} encoding using
      \samp{<U+xxxx>} escapes.

      \item There is a new function \code{infoRDS()} providing information
      about the serialization format of a serialized object.

      \item S3 method lookup now by default skips the elements of the
      search path between the global and base environments.

      \item Added an argument \code{add_datalist(*, small.size = 0)} to
      allow the creation of a \file{data/datalist} file even when the
      total size of the data sets is small.

      \item The backquote function \code{bquote()} has a new argument
      \code{splice} to enable splicing a computed list of values into an
      expression, like \code{,@} in LISP's backquote.

      \item The formula interface to \code{t.test()} and
      \code{wilcox.test()} has been extended to handle one-sample and
      paired tests.

      \item The \code{palette()} function has a new default set of
      colours (which are less saturated and have better accessibility
      properties).  There are also some new built-in palettes, which
      are listed by the new \code{palette.pals()} function.  These
      include the old default palette under the name \code{"R3"}. Finally,
      the new \code{palette.colors()} function allows a subset of
      colours to be selected from any of the built-in palettes.

      \item \code{n2mfrow()} gains an option \code{asp = 1} to specify the
      aspect ratio, fulfilling the wish and extending the proposal of
      Michael Chirico in \PR{17648}.

      \item For \code{head(x, n)} and \code{tail()} the default and
      other S3 methods notably for \emph{vector} \code{n}, e.g. to get a
      \dQuote{corner} of a matrix, has been extended to \code{array}'s
      of higher dimension thanks to the patch proposal by Gabe Becker in
      \PR{17652}.  Consequently, optional argument \code{addrownums} is
      deprecated and replaced by the (more general) argument
      \code{keepnums}.  An invalid second argument \code{n} now leads
      to typically more easily readable error messages.

      \item New function \code{.class2()} provides the full character
      vector of class names used for S3 method dispatch.

      \item Printing \code{methods(..)} now uses a new \code{format()} method.

      \item \code{sort.list(x)} now works for non-atomic objects
      \code{x} and \code{method = "auto"} (the default) or
      \code{"radix"} in cases \code{order(x)} works, typically via a
      \code{xtfrm()} method.

      \item Where they are available, \code{writeBin()} allows
      long vectors.% (those of length \eqn{\ge 2^{31}}{>= 2^31}).

      \item New function \code{deparse1()} produces one string, wrapping
      \code{deparse()}, to be used typically in
      \code{deparse1(substitute(*))}, e.g., to fix \PR{17671}.

      \item \code{wilcox.test()} enhancements: In the (non-paired)
      two-sample case, \code{Inf} values are treated as very large for
      robustness consistency.  If exact computations are used, the
      result now has \code{"exact"} in the \code{method} element of its
      return value.  New arguments \code{tol.root} and
      \code{digits.rank} where the latter may be used for stability to
      treat very close numbers as ties.

      \item \code{readBin()} and \code{writeBin()} now report an error
      for an invalid \code{endian} value.  The affected code needs to be
      fixed with care as the old undocumented behavior was to swap
      endian-ness in such cases.

      \item \code{sequence()} is now an S3 generic with an internally
      implemented default method, and gains arguments to generate more
      complex sequences.  Based on code from the \pkg{S4Vectors}
      Bioconductor package and the advice of Hervé Pagès.

      \item \code{print()}'s default method and many other methods (by
      calling the default eventually and passing \code{...}) now make
      use of a new optional \code{width} argument, avoiding the need for
      the user to set and reset \code{options("width")}.

      \item \code{memDecompress()} supports the RFC 1952 format
      (e.g.\sspace{}in-memory copies of \command{gzip}-compressed files)
      as well as RFC 1950.

      \item \code{memCompress()} and \code{memDecompress()} support long
      raw vectors for types \code{"gzip"} and \code{"zx"}.

      \item \code{sweep()} and \code{slice.index()} can now use names
      of dimnames for their \code{MARGIN} argument (\code{apply} has
      had this for almost a decade).

      \item New function \code{proportions()} and
      \code{marginSums()}. These should replace the unfortunately named
      \code{prop.table()} and \code{margin.table()}. They are drop-in
      replacements, but also add named-margin functionality. The old
      function names are retained as aliases for back-compatibility.

      \item Functions \code{rbinom()}, \code{rgeom()}, \code{rhyper()},
      \code{rpois()}, \code{rnbinom(),} \code{rsignrank()} and
      \code{rwilcox()} which have returned integer since \R 3.0.0 and hence
      \code{NA} when the numbers would have been outside the integer range,
      now return double vectors (without NAs, typically) in these cases.

      \item \code{matplot(x,y)} (and hence \code{matlines()} and
      \code{matpoints()}) now call the corresponding methods of
      \code{plot()} and \code{lines()}, e.g, when \code{x} is a
      \code{"Date"} or \code{"POSIXct"} object; prompted by Spencer Graves'
      suggestion.

      \item \code{stopifnot()} now allows customizing error messages via
      argument names, thanks to a patch proposal by Neal Fultz in \PR{17688}.

      \item  \code{unlink()} gains a new argument \code{expand} to disable
      wildcard and tilde expansion.  Elements of \code{x} of value
      \code{"~"} are now ignored.

      \item \code{mle()} in the \code{stats4} package has had its
      interface extended so that arguments to the negative
      log-likelihood function can be one or more vectors, with similar
      conventions applying to bounds, start values, and parameter values
      to be kept fixed.  This required a minor extension to class
      \code{"mle"}, so saved objects from earlier versions may need to
      be recomputed.

      \item The default for \code{pdf()} is now
      \code{useDingbats = FALSE}.

      \item The default fill colour for \code{hist()} and
      \code{boxplot()} is now \code{col = "lightgray"}.

      \item The default order of the levels on the y-axis for
      \code{spineplot()} and \code{cdplot()} has been reversed.

      \item If the \env{R_ALWAYS_INSTALL_TESTS} environment variable is
      set to a true value, \command{R CMD INSTALL} behaves as if
      the \option{--install-tests} option is always specified. Thanks to
      Reinhold Koch for the suggestion.

      \item New function \code{R_user_dir()} in package \pkg{tools}
      suggests paths appropriate for storing \R-related user-specific
      data, configuration and cache files.

      \item \code{capabilities()} gains a new logical option \code{Xchk}
      to avoid warnings about X11-related capabilities.

      \item The internal implementation of \pkg{grid} units has changed,
      but the only visible effects at user-level should be
      \itemize{
	\item a slightly different print format for some units
	(especially unit arithmetic),
	\item faster performance (for unit operations) and
	\item two new functions \code{unitType()} and \code{unit.psum()}.
      }
      Based on code contributed by Thomas Lin Pedersen.

      \item When internal dispatch for \code{rep.int()}
      and \code{rep_len()} fails, there is an attempt to dispatch on the
      equivalent call to \code{rep()}.

      \item Object \code{.Machine} now contains new \code{longdouble.*}
      entries (when \R uses long doubles internally).

      \item \code{news()} has been enhanced to cover the news on \R 3.x
      and 2.x.

       \item For consistency, \code{N <- NULL; N[[1]] <- val} now turns
       \code{N} into a \code{list} also when \code{val)} has length one.
       This enables \code{dimnames(r1)[[1]] <- "R1"} for a 1-row matrix
       \code{r1}, fixing \PR{17719} reported by Serguei Sokol.

       \item \code{deparse(..)}, \code{dump(..)}, and \code{dput(x,
	 control = "all")} now include control option \code{"digits17"}
       which typically ensures 1:1 invertibility.  New option
       \code{control = "exact"} ensures numeric exact invertibility
       via \code{"hexDigits"}.

      \item When loading data sets via \code{read.table()},
       \code{data()} now uses \samp{LC_COLLATE=C} to ensure
       locale-independent results for possible string-to-factor
       conversions.

      \item A server socket connection, a new connection type
      representing a listening server socket, is created via
      \code{serverSocket()} and can accept multiple socket connections
      via \code{socketAccept()}.

      \item New function \code{socketTimeout()} changes the connection
      timeout of a socket connection.

      \item The time needed to start a homogeneous \samp{PSOCK} cluster on
      \samp{localhost} with many nodes has been significantly reduced
      (package \pkg{parallel}).

      \item New \code{globalCallingHandlers()} function to establish
      global condition handlers.  This allows registering default
      handlers for specific condition classes. Developed in
      collaboration with Lionel Henry.

      \item New function \code{tryInvokeRestart()} to invoke a specified
      restart if one is available and return without signaling an error
      if no such restart is found.  Contributed by Lionel Henry in
      \PR{17598}.

      \item \code{str(x)} now shows the length of \code{attributes} in some
      cases for a data frame \code{x}.

      \item \code{Rprof()} gains a new argument \code{filter.callframes}
      to request that intervening call frames due to lazy evaluation or
      explicit \code{eval()} calls be omitted from the recorded profile
      data.  Contributed by Lionel Henry in \PR{17595}.

      \item The handling of \code{$\{FOO-bar\}} and \code{$\{FOO:-bar\}}
      in \file{Renviron} files now follows POSIX shells (at least on a
      Unix-alike), so the first treats empty environment variables as
      set and the second does not.  Previously both ignored empty
      variables.  There are several uses of the first form in
      \file{etc/Renviron}.

      \item New \code{classes} argument for \code{suppressWarnings()}
      and \code{suppressMessages()} to selectively suppress only
      warnings or messages that inherit from particular classes.
      Based on patch from Lionel Henry submitted with \PR{17619}.

      \item New function \code{activeBindingFunction()} retrieves the
      function of an active binding.

      \item New \code{"cairoFT"} and \code{"pango"} components in the
      output of \code{grSoftVersion()}.

      \item New argument \code{symbolfamily} in cairo-based graphics
      devices and new function \code{cairoSymbolFont()} that can be used
      to provide the value for that argument.
    }
  }% end{ NEW FEATURES }

  \subsection{Windows}{
    \itemize{
      \item \command{Rterm} now works also when invoked from MSYS2
      terminals.  Line editing is possible when command \command{winpty} is
      installed.

      \item \code{normalizePath()} now resolves symbolic links and
      normalizes case of long names of path elements in case-insensitive
      folders (\PR{17165}).

      \item \code{md5sum()} supports UTF-8 file names with characters
      that cannot be translated to the native encoding (\PR{17633}).

      \item \command{Rterm} gains a new option \option{--workspace} to
      specify the workspace to be restored.  This allows equals to be
      part of the name when opening \emph{via} Windows file associations
      (reported by Christian Asseburg).

      \item \command{Rterm} now accepts \code{ALT+xxx} sequences also
      with NumLock on.  Tilde can be pasted with an Italian keyboard
      (\PR{17679}).

      \item \R falls back to copying when junction creation fails during
      package checking (patch from Duncan Murdoch).
   }
  }

  \subsection{DEPRECATED AND DEFUNCT}{
    \itemize{
      \item Make macro \samp{F77_VISIBILITY} has been removed
      and replaced by \samp{F_VISIBILITY}.

      \item Make macros \samp{F77}, \samp{FCPIFCPLAGS} and
      \samp{SHLIB_OPENMP_FCFLAGS} have been removed and replaced by
      \samp{FC}, \samp{FPICFLAGS} and \samp{SHLIB_OPENMP_FFLAGS}
      respectively.  (Most \command{make} programs will set \samp{F77}
      to the value of \samp{FC}, which is set for package compilation.
      But portable code should not rely on this.)

      \item The deprecated support for specifying C++98 for package
      installation has been removed.

      \item \command{R CMD config} no longer knows about the
      unused settings \samp{F77} and \samp{FCPIFCPLAGS}, nor
      \samp{CXX98} and similar.

      \item Either PCRE2 or PCRE1 >= 8.32 (Nov 2012) is required: the
      deprecated provision for 8.20--8.31 has been removed.

      \item Defunct functions \code{mem.limits()}, \code{.readRDS()},
      \code{.saveRDS()}, \code{.find.package()}, and \code{.path.package()}
      from package \pkg{base}
      and \code{allGenerics()}, \code{getAccess()}, \code{getAllMethods()},
      \code{getClassName()}, \code{getClassPackage()}, \code{getExtends()},
      \code{getProperties()}, \code{getPrototype()},
      \code{getSubclasses()}, \code{getVirtual()}, \code{mlistMetaName()},
      \code{removeMethodsObject()}, \code{seemsS4Object()},
      \code{traceOff()}, and \code{traceOn()} from \pkg{methods} have been
      removed.
    }
  }

  \subsection{C-LEVEL FACILITIES}{
    \itemize{
      \item \code{installChar} is now remapped in \file{Rinternals.h} to
      \code{installTrChar}, of which it has been a wrapper since
      \R\sspace{}3.6.0.  Neither are part of the API, but packages using
      \code{installChar} can replace it if they depend on \samp{R >= 3.6.2}.

      \item Header \file{R_ext/Print.h} defines \samp{R_USE_C99_IN_CXX}
      and hence exposes \code{Rvprintf} and \code{REvprintf} if used
      with a C++11 (or later) compiler.

      \item There are new Fortran subroutines \code{dblepr1},
      \code{realpr1} and \code{intpr1} to print a scalar variable
      (\command{gfortran} 10 enforces the distinction between scalars
      and length-one arrays).  Also \code{labelpr} to print just a label.

      \item \code{R_withCallingErrorHandler} is now available for
      establishing a calling handler in C code for conditions inheriting
      from class \code{error}.
    }
  }

  \subsection{INSTALLATION on a UNIX-ALIKE}{
    \itemize{
      \item User-set \samp{DEFS} (e.g., in \file{config.site}) is now
      used for compiling packages (including base packages).

      \item There is a new variant option \option{--enable-lto=check}
      for checking consistency of BLAS/LAPACK/LINPACK calls --- see
      \sQuote{Writing R Extensions}.

      \item A C++ compiler default is set only if the C++11 standard is
      supported: it no longer falls back to C++98.

      \item PCRE2 is used if available.  To make use of PCRE1 if PCRE2
      is unavailable, configure with option \option{--with-pcre1}.

      \item The minimum required version of \code{libcurl} is now 7.28.0
      (Oct 2012).

      \item New make target \command{distcheck} checks
      \itemize{
	\item \R can be rebuilt from the tarball created by
	\command{make dist},
	\item the build from the tarball passes \command{make check-all},
	\item the build installs and uninstalls,
	\item the source files are properly cleaned by \command{make distclean}.
      }
    }
  }

  \subsection{UTILITIES}{
    \itemize{
      \item \command{R --help} now mentions the option \command{--no-echo}
      (renamed from \command{--slave}) and its previously undocumented
      short form \command{-s}.

      \item \command{R CMD check} now optionally checks
      \command{configure} and \command{cleanup} scripts for
      non-Bourne-shell code (\sQuote{bashisms}).

      \item \command{R CMD check --as-cran} now runs \code{\\donttest}
      examples (which are run by \code{example()}) instead of
      instructing the tester to do so.  This can be temporarily
      circumvented during development by setting environment variable
      \env{_R_CHECK_DONTTEST_EXAMPLES_} to a false value.
    }
  }

  \subsection{PACKAGE INSTALLATION}{
    \itemize{
      \item There is the beginnings of support for the recently approved
      C++20 standard, specified analogously to C++14 and C++17.  There is
      currently only limited support for this in compilers, with flags
      such as \option{-std=c++20} and \option{-std=c++2a}.  For the time
      being the \command{configure} test is of accepting one of these
      flags and compiling C++17 code.
    }
  }

  \subsection{BUG FIXES}{
    \itemize{
      \item \code{formula(x)} with \code{length(x) > 1} character vectors,
      is deprecated now.  Such use has been rare, and has \sQuote{worked}
      as expected in some cases only.  In other cases, wrong \code{x} have
      silently been truncated, not detecting previous errors.

      \item Long-standing issue where the X11 device could lose events
      shortly after startup has been addressed (\PR{16702}).

      \item The \code{data.frame} method for \code{rbind()} no longer
      drops \code{<NA>} levels from factor columns by default
      (\PR{17562}).

      \item \code{available.packages()} and hence \code{install.packages()}
      now pass their \code{...} argument to \code{download.file()},
      fulfilling the wish of \PR{17532}; subsequently,
      \code{available.packages()} gets new argument \code{quiet}, solving
      \PR{17573}.

      \item \code{stopifnot()} gets new argument \code{exprObject} to allow
      an \R object of class \code{expression} (or other \sQuote{language})
      to work more consistently, thanks to suggestions by Suharto Anggono.

      \item \code{conformMethod()} now works correctly in cases containing
      a \dQuote{\code{&&} logic} bug, reported by Henrik Bengtsson.  It now
      creates methods with \code{"missing"} entries in the signature.
      Consequently, \code{rematchDefinition()} is amended to use
      appropriate \code{.local()} calls with named arguments where needed.

      \item \code{format.default(*, scientific = FALSE)} now corresponds to
      a practically most extreme \code{options(scipen = n)} setting rather
      than arbitrary \code{n = 100}.

      \item \code{format(as.symbol("foo"))} now works (returning \code{"foo"}).

      \item \code{postscript(.., title = *)} now signals an error when
      the title string contains a character which would produce corrupt
      PostScript, thanks to \PR{17607} by Daisuko Ogawa.

      \item Certain \code{Ops} (notably comparison such as \code{==}) now
      also work for 0-length data frames, after reports by Hilmar Berger.

      \item \code{methods(class = class(glm(..)))} now warns more usefully
      and only once.

      \item \code{write.dcf()} no longer mangles field names (\PR{17589}).

      \item Primitive replacement functions no longer mutate a
      referenced first argument when used outside of a complex
      assignment context.

      \item  A better error message for \code{contour(*, levels = Inf)}.

      \item The return value of \code{contourLines()} is no longer
      \code{invisible()}.

      \item The Fortran code for calculating the \code{coefficients}
      component in \code{lm.influence()} was very inefficient. It has
      (for now) been replaced with much faster \R{} code (\PR{17624}).

      \item \code{cm.colors(n)} \emph{etc} no longer append the code for
      \code{alpha = 1}, \code{"FF"}, to all colors.  Hence all eight
      \code{*.colors()} functions and \code{rainbow()} behave
      consistently and have the same non-explicit default (\PR{17659}).

      \item \code{dnorm} had a problematic corner case with \code{sd ==
      -Inf} or negative \code{sd} which was not flagged as an error in
      all cases. Thanks to Stephen D. Weigand for reporting and Wang
      Jiefei for analyzing this; similar change has been made in
      \code{dlnorm()}.

      \item The optional \code{iter.smooth} argument of
      \code{plot.lm()}, (the \code{plot()} method for \code{lm} and
      \code{glm} fits) now defaults to \code{0} for all \code{glm} fits.
      Especially for binary observations with high or low fitted
      probabilities, this effectively deleted all observations of 1 or
      0.  Also, the type of residuals used in the \code{glm} case has
      been switched to \code{"pearson"} since deviance residuals do not
      in general have approximately zero mean.

      \item In \code{plot.lm}, Cook's distance was computed from unweighted
      residuals, leading to inconsistencies.  Replaced with usual weighted
      version. (\PR{16056})

      \item Time-series \code{ts(*, start, end, frequency)} with
      fractional \code{frequency} are supported more consistently;
      thanks to a report from Johann Kleinbub and analysis and patch by
      Duncan Murdoch in \PR{17669}.

      \item In case of errors \code{mcmapply()} now preserves attributes
      of returned \code{"try-error"} objects and avoids simplification,
      overriding \code{SIMPLIFY} to \code{FALSE}. (\PR{17653})

      \item \code{as.difftime()} gets new optional \code{tz = "UTC"}
      argument which should fix behaviour during
      daylight-savings-changeover days, fixing \PR{16764}, thanks to
      proposals and analysis by Johannes Ranke and Kirill Müller.

      \item \code{round()} does a better job of rounding
      \emph{\dQuote{to nearest}} by \emph{measuring} and
      \emph{\dQuote{to even}}; thanks to a careful algorithm originally
      prompted by the report from Adam Wheeler and then others, in
      \PR{17668}.  \cr \code{round(x, dig)} for \emph{negative} digits
      is much more rational now, notably for large \eqn{|dig|}.

      \item Inheritance information on S4 classes is maintained more
      consistently, particularly in the case of class unions (in part
      due to \PR{17596} and a report from Ezra Tucker).

      \item \code{is()} behaves more robustly when its argument
      \code{class2} is a \code{classRepresentation} object.

      \item The warning message when attempting to export an nonexistent
      class is now more readable; thanks to Thierry Onkelinx for
      recognizing the problem.

      \item \code{choose()} misbehaved in corner cases where it switched
      \code{n - k} for \code{k} and \code{n} was only \emph{nearly} integer
      (report from Erik Scott Wright).

      \item \code{mle()} in the \code{stats4} package had problems
      combining use of box constraints and fixed starting values (in
      particular, confidence intervals were affected).

      \item Operator \code{?} now has lower precedence than \code{=} to
      work as documented, so \code{=} behaves like \code{<-} in help
      expressions (\PR{16710}).

      \item \code{smoothEnds(x)} now returns \code{integer} type in
      \emph{both} cases when \code{x} is \code{integer}, thanks to a
      report and proposal by Bill Dunlap \PR{17693}.

      \item The \pkg{methods} package does a better job of tracking
      inheritance relationships across packages.

      \item \code{norm(diag(c(1, NA)), "2")} now works.

      \item \code{subset()} had problems with 0-col dataframes (reported
      by Bill Dunlap, \PR{17721}).

      \item Several cases of integer overflow detected by the
      \sQuote{undefined behaviour sanitizer} of \command{clang} 10 have
      been circumvented.  One in \code{rhyper()} may change the
      generated value for large input values.

      \item \code{dotchart()} now places the y-axis label (\code{ylab})
      much better, not overplotting labels, thanks to a report and
      suggestion by Alexey Shipunov.

      %% detected by clang-ASAN in examples/tests of adehabitatHR.
      \item A rare C-level array overflow in \code{chull()} has been
      worked around.

      \item Some invalid specifications of the day-of-the-year
      (\emph{via} \code{\%j}, e.g.\sspace{}day 366 in 2017) or week
      plus day-of-the-week are now detected by \code{strptime()}.
      They now return \code{NA} but give a warning as they may have
      given random results or corrupted memory in earlier versions of \R.

      \item \code{socketConnection(server = FALSE)} now respects the
      connection timeout also on Linux.

      \item \code{socketConnection(server = FALSE)} no longer leaks a
      connection that is available right away without waiting (e.g. on
      \samp{localhost}).

      \item Socket connections are now robust against spurious readability
      and spurious availability of an incoming connection.

      \item \code{blocking = FALSE} is now respected also on the server side
      of a socket connection, allowing non-blocking read operations.

      \item \code{anova.glm()} and \code{anova.glmlist()} computed
      incorrect score (Rao) tests in no-intercept cases. (André
      Gillibert, \PR{17735})

      \item \code{summaryRprof()} now should work correctly for the
      \code{Rprof(*, memory.profiling=TRUE)} case with small chunk size (and
      \code{"tseries"} or similar) thanks to a patch proposal by Benjamin
      Tyner, in \PR{15886}.

      \item \code{xgettext()} ignores strings passed to
      \code{ngettext()}, since the latter is handled by
      \code{xngettext()}. Thanks to Daniele Medri for the report and all
      the recent work he has done on the Italian translations.

      \item \code{data(package = "P")} for \code{P} in \pkg{base} and
      \pkg{stats} no longer reports the data sets from package
      \pkg{datasets} (which it did for back compatibility for 16 years),
      fixing \PR{17730}.

      \item \code{x[[Inf]]} (returning \code{NULL}) no longer leads to
      undefined behavior, thanks to a report by Kirill Müller in
      \PR{17756}.  Further, \code{x[[-Inf]]} and \code{x[[-n]]} now give
      more helpful error messages.

      \item \code{Gamma()} family sometimes had trouble storing
      link name \PR{15891}
    }
  }

  \subsection{BUG FIXES (Windows)}{
    \itemize{
      \item \code{Sys.glob()} now supports all characters
      from the Unicode Basic Multilingual Plane, no longer corrupting
      some (less commonly used) characters (\PR{17638}).

      \item \command{Rterm} now correctly displays
      multi-byte-coded characters representable in the current native
      encoding (at least on Windows 10 they were sometimes omitted,
      \PR{17632}).

      \item \code{scan()} issues with UTF-8 data when running in a DBCS
      locale have been resolved (\PR{16520}, \PR{16584}).

      \item \command{Rterm} now accepts enhanced/arrow keys also with
      ConPTY.

      \item \R can can now be started \emph{via} the launcher icon in a
      user documents directory whose path is not representable in the
      system encoding.

      \item \code{socketConnection(server = FALSE)} now returns instantly
      also on Windows when connection failure is signalled.

      \item Problems with UTF-16 surrogate pairs have been fixed in
      several functions, including \command{tolower()} and
      \command{toupper()} (\PR{17645}).
    }
  }
}

\section{CHANGES in previous versions}{
  \itemize{
    \item Older news can be found in text format in files
    \ifelse{html}{\href{../NEWS.0}{NEWS.0}, \href{../NEWS.1}{NEWS.1},
      \href{../NEWS.2}{NEWS.2} and
      and \href{../NEWS.3}{NEWS.3}}{\file{NEWS.0}, \file{NEWS.1},
      \file{NEWS.2} and \file{NEWS.3}}
    in the \file{doc} directory.  News in HTML format for
    \R  versions 3.x and from 2.10.0 to 2.15.3 is available at
    \ifelse{html}{\url{NEWS.3.html}}{\file{doc/html/NEWS.3.html}}
    and
    \ifelse{html}{\url{NEWS.2.html}}{\file{doc/html/NEWS.2.html}}.
  }
}
