static CharSequence subCharSequence(CharSequence s, int x) {
  ret subCharSequence(s, x, s == null ? 0 : s.length());
}

static CharSequence subCharSequence(CharSequence s, int x, int y) {
  if (s == null) null;
  if (x < 0) x = 0;
  if (x >= s.length()) return "";
  if (y < x) y = x;
  if (y > s.length()) y = s.length();
  ret s.subSequence(x, y);
}