Returns a subset of the current MutableMap starting from a given key location up to, but not including, the element at the provided length from the starting key location

public function slice(
  int $start,
  int $len,
): MutableMap<Tk, Tv>;

$start is 0-based. $len is 1-based. So slice(0, 2) would return the keys and values at key location 0 and 1.

The returned MutableMap will always be a proper subset of the current MutableMap.