This documents significant changes in the 93u+m branch of AT&T ksh93.
For full details, see the git log at:
	https://github.com/modernish/ksh

Any uppercase BUG_* names are modernish shell bug IDs.

2020-05-16:

- Fix 'test -t 1', '[ -t 1 ]', '[[ -t 1 ]]' in command substitutions.
  Standard output (file descriptor 1) tested as being on a terminal within a
  command substitution, which makes no sense as the command substitution is
  supposed to be catching standard output.
	v=$(echo begincomsub
	    [ -t 1 ] && echo oops
	    echo endcomsub)
	echo "$v"
  This now does not output "oops".

2020-05-14:

- Fix syncing history when print -s -f is used. For example, the
  following now correctly adds a 'cd' command to the history:
	print -s -f 'cd -- %q\n' "$PWD"
  Ref.:	https://github.com/att/ast/issues/425
	https://github.com/att/ast/pull/442

- Fix BUG_PUTIOERR: Output builtins now correctly detect and report
  input/output errors. This allows scripts to check for a nonzero exit
  status on the 'print', 'printf' and 'echo' builtins and prevent possible
  infinite loops if SIGPIPE is ignored.

- Add a convenient bin/run_ksh_tests script to the source tree that
  sets up the necessary environment and runs the ksh regression tests.

2020-05-13:

- Fix BUG_CASELIT: an undocumented 'case' pattern matching misbehaviour that
  goes back to the original Bourne shell, but wasn't discovered until 2018.
  If a pattern doesn't match as a pattern, it was tried again as a literal
  string. This broke common validation use cases, e.g.:
      n='[0-9]'
      case $n in
      ( [0-9] )  echo "$n is a number" ;;
      esac
  would output "[0-9] is a number" as the literal string fallback matches the
  pattern. As this misbehaviour was never documented anywhere (not for Bourne,
  ksh88, or ksh93), and it was never replicated in other shells (not even in
  ksh88 clones pdksh and mksh), it is unlikely any scripts rely on it.
     Of course, a literal string fallback, should it be needed, is trivial to
  implement correctly without this breakage:
      case $n in
      ( [0-9] | "[0-9]")  echo "$n is a number or the number pattern" ;;
      esac
  Ref.: https://github.com/att/ast/issues/476

- Fix BUG_REDIRIO: ksh used to redirect standard output by default when no
  file descriptor was specified with the rarely used '<>' reading/writing
  redirection operator. It now redirects standard input by default, as POSIX
  specifies and as all other POSIX shells do. To redirect standard output
  for reading and writing, you now need '1<>'.
  Ref.:	https://github.com/att/ast/issues/75
	http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_07