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

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

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

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