static S unquoteMultiline(S s) {
  if (s == null) null;
  if (startsWith(s, '[')) {
    int i = 1;
    while (i < s.length() && s.charAt(i) == '=') ++i;
    if (i < s.length() && s.charAt(i) == '[') {
      S m = s.substring(1, i);
      if (s.endsWith("]" + m + "]"))
        ret s.substring(i+1, s.length()-i-1);
    }
  }
  
  ret s; // not multiline-quoted - return original
}

Began life as a copy of #1001735