v vs. u m

user-visible changes between 93v- 2014-12-24 and 93u+m*

All of these sections are incomplete

Bugs in u+m with fixes in v-

TODO: Add list of applicable bugfixes in 93v- not yet backported to 93u+m. The 93v- RELEASE file lists at least some of these bugfixes:
https://github.com/ksh93/ksh93-history/blob/2016-01-10/src/cmd/ksh93/RELEASE

<>file default fd
function f { return; } is now equal to function f { return "$?"; }. (not sure if bug or feature but now agrees with other shells.)

~{fd} and ~{var} expansions. (undocumented)
__ special variable. (undocumented)
.sh.sig special compound variable. Exposes the siginfo_t structure. (undocumented)
set -K numeric and reverse sorting for various kinds of arrays or positional parameters.
typeset -c new=obj Like typeset -m (move) but performs an object copy from obj to new. (undocumented)
A short-lived feature in which ${ .sh.value=result; } could be used to return a value was added then quietly removed. reference
The grep and poll builtins.
-m method option that reads a compound variable in a specific format. Two formats provided: ksh and json
JSON compound variable output with print -j and printf "%(json)B"
JSON input with read -m json
enum constants can have .DIG, .MAX, .MIN sub-variables.
Floating-point variables can be following by .DIG, .MAX, .MIN, .EPSILON, .INT_MAX, .INT_MIN, or .MAX_10_EXP to give values corresponding to the floating type of the variable.
Integer variables can be followed by .DIG, .MAX, or .MIN in arithmetic expression so give the values corresponding to that integer type.
Math constants such as E, LOG2E, LOG10E, LN2, PI, PI_2, PI_4, SQRT2, SQRT1_2