static S substring(S s, int x) {
  ret substring(s, x, strL(s));
}

static S substring(S s, int x, int y) {
  if (s == null) return null;
  if (x < 0) x = 0;
  int n = s.length();
  if (y < x) y = x;
  if (y > n) y = n;
  if (x >= y) ret "";
  return s.substring(x, y);
}

ifclass IntRange
static S substring(S s, IntRange r) {
  ret r == null ? null : substring(s, r.start, r.end);
}
endif

// convenience method for quickly dropping a prefix
sS substring(S s, CharSequence l) {
  ret substring(s, l(l));
}

Began life as a copy of #1001853