R53a is a snapshot/feature release:

• Fix spelling
• Unbreak multi-line command history broken by history flush
• Fix redefining POSIX functions that were Korn functions before
• Fix bounds checks in Vi editing mode
• Handle combining characters at end of string or output correctly
• Fix ${!#} ${!?} ${!-} (POSIX, prompted by izabera)
• Fix shf.c-internal buffer overread on printing digits
• Fix a typo in the testsuite
• Increase default edit line size (unless MKSH_SMALL)
• Improve description of Emacs mode keybindings, especially ^U
• Abort read builtin in case of read(2) errors
• Fix most of the ambiguous corner cases related to ${[pfx]var[op[word]]} (${@:-1} still unsupported)
• Contribute some more testsuite coverage
• WDS_TPUTS now emits QCHAR newline reentrant-safe
• Fix var=<< implementation (LP#1380389)
• Make XSI test(1) extensions behave as if they were POSIX
• Add $(<<<x) and $(<<EOF…) implementation
• Lower minimum screen size accepted as “sane” from the OS to 4×2
• Simplify tilde-expanded parameters
• Fix default PS1 for substring matches
• Apply defer-builtin-with-arguments logic to realpath builtin
• Rework string pooling (own vs. compiler’s) (LP#1580348)
• Feature: print -A, prints arguments as characters
• Replace <<< and >>> as ROL and ROR operators with their new ^< and ^> spelling as per this proposal
• Clear-to-EOL under tmux to work around its anti-feature
• Remove support for using file descriptors with more than a single digit, in preparation for named file descriptors
• Correct, but simplify (at the potential cost of more tty I/O than strictly necessary, though never redundant and (probably) not more than before when it was miscalculated), line clearing and redrawing
• Implement new evaluate-region editing command Esc+Ctrl-E
• Prefer external rename utility over the recovery builtin
• Remove redundant full-line redraws
• Fix errorlevel of ‘.’ (“dot” special builtin) when the sourced script does not run any commands, for POSIX compliance
• Refactor op tokens and edchars to shave off some more bytes
• Fix some bugs in the manpage and some occasional/minor code bugs
• Mark tests requiring new perl as !need-pass
• Add $KSH_MATCH and, to make it usable, ${foo@/bar/baz}
• Fix bogus patch from OpenBSD: only NULL the global source in unwind when actually reclaiming its Area
• Mention in the manpage that integer bases go up to 36
• Fix /= operator broken during refactoring