static Substring substringObject(CharSequence s, int x) {
  ret substringObject(s, x, l(s));
}

static Substring substringObject(CharSequence s, int x, int y) {
  if (s == null) null;
  if (x < 0) x = 0;
  if (x > s.length()) x = s.length();
  if (y < x) y = x;
  if (y > s.length()) y = s.length();
  ret new Substring(s, x, y);
}

Began life as a copy of #1002637