Your code does not work when $2 is less than one or greater than 255.

alias list {
  if ($2 !isnum) || (0 > $2 || $2 > 255) || (!$isid) return
  var %a $regsubex($$1,/ $+ $chr($2) $+ /gi,$+($chr(44),$chr(32)))
  if ($regex($prop,^(a|c)(a|c)?$)) {
    if (a isin $prop) %a = $instok(%a,and,-1,32)
    if (c isin $prop) %a = $upper($left(%a,1-)) $+ $right(%a,-1)
  }
  return %a
}