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
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.
$start- The starting key of the current
KeyedIterableto begin the returned
$len- The length of the returned