Code:
dialog -l example {
  title "Example"
  size -1 -1 102 68
  option dbu
  edit "", 1, 1 1 100 50, multi autovs vsbar
  button "Echo", 2, 34 53 37 12
}

on *:dialog:example:sclick:2:{
  var %i = 1
  while ($did($dname, 1, %i)) { 
    echo -a $ifmatch
    var %full = %full $ifmatch
    inc %i
  }
  echo -a Reconstructed: %full
}

alias example dialog -m example example


Type /example and type text.

Make one long string (longer than the editbox allows per one line), and hit echo. It'll show it broken up. Sure, you say, use $+.. but...

Type a long string, and maybe 5-6 chars before the end of that line, hit space, and start typing again. Do a very long string after. You have a legitimate break here, and a $+ would join the two spaced strings.

Now copy either of the examples above fom the editbox and paste into notepad. You'll see it's reconstructed correctly.