sS unquote_relaxedMLS(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) == '[') {
      String m = s.substring(1, i);
      int n = s.length();
      if (s.endsWith("]" + m + "]"))
        n -= i+1;
      ret s.substring(i+1, n);
    }
  }
  ret unquoteSingleOrDoubleQuotes(s);
}

Began life as a copy of #1001735