UTILITIES:

• tools/fetch-recommended can be used instead of
  tools/rsync-recommended to fetch recommended packages into R
  sources using curl on systems without rsync or behind firewalls.

PACKAGE INSTALLATION:

• C++ standard specifications (CXX_STD = in src/Makevars* and in
  the SystemRequirements field of the DESCRIPTION file) are now
  checked more thoroughly. Invalid values are still ignored but
  now give a warning, as do contradictory specifications.

• (Preliminary) support for C++26 has been extended to Windows.

• A non-zero exit status from cleanup, cleanup.win or cleanup.ucrt,
  if requested via options --clean or --preclean, is now reported
  with a warning.

BUG FIXES:

• all.equal(obj, simple, check.class=FALSE) now is true, also when
  simple is a bare atomic vector and obj has a simple class, fixing
  the first part of PR#18971 thanks to Jan Gorecki.

• str(x, give.attr=FALSE) no longer shows attributes when x is a
  zero length "Date" or "POSIXt" object.

• Tweaks to binning for bw.SJ() and bw.ucv() in the very rare case
  of data which have an extremely small range compared to their
  absolute values, e.g., x <- 6e9 + 6:9.

• Formatting book-type bibentry objects now converts LaTeX accents
  also in the publisher and series fields.

• model.frame(~1, list(), na.action=na.pass) and similar
  “border-line” uses no longer produce invalid data frames, fixing
  PR#18977, reported with patch by Mikael Jagan.

• length(<POSIXlt>) <- v is more careful about balancing, notably
  when v is not integer, thanks to Suharto Anggono's remarks on the
  mailing list R-devel.

• approx(<x_with_ties>, <y_with_NA>, na.rm = FALSE) now should
  always call the ties() function, fixing PR#17604 reported by Bill
  Dunlap.

• besselJ(1, 1e-15) and similar now give correct results, thanks to
  Leo Mada and other “R-help”ers.

• vignette(<pkg>::<topic>) is now a documented usage variant and
  confines vignette retrieval to the specified package.

• pretty(ch) again correctly works with ch a character vector of
  numbers.

• persp() labels the three axes correctly also when C level
  atan2pi() is available, fixing PR#19007 by Klaus Schliep.

• Large (tall) subscripts in plotmath expressions are now
  positioned correctly. They were being positioned too high.

• Ops group (Arith, Compare,..) methods for matrix-"ts" now do
  return (zero length) matrices even when the two series do not
  overlap, a very partial fix of PR#18972 which is to be fully
  addressed later.