• File share/texmf/tex/latex/jss.cls has been updated to work with
  LaTeX versions since Oct 2020.

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

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

INSTALLATION on a UNIX-ALIKE:

• If an external BLAS is specified by --with-blas=foo or via
  environment variable 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
  --with-blas=yes was specified.

BUG FIXES:

• all.equal(x,y) now "sees" the two different NAs in factors,
  thanks to Bill Dunlap and others in PR#17897.

• (~ 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.

• .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.

• 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.

• iconvlist() now also works on MUSL based (Linux) systems, from a
  report and patch suggestion by Wesley Chan in PR#17970.

• round() and 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.

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

• p.adjust(numeric(), n=0) now works, fixing PR#18002.

• identical(x,y) no longer prints "Unknown Type .." for typeof(x) == "..." objects.

• Fix (auto-)print()ing of named complex vectors, see PR#17868 and
  PR#18019.

• all.equal(<language>, <...>) now works, fixing PR#18029.

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

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

• 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.