Returns a subset of the current
ConstSet 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, ): ConstSet<Tv>;
$start is 0-based.
$len is 1-based. So
2) would return the
elements at key 0 and 1.
int $start- The starting value in the current
ConstSetfor the returned
int $len- The length of the returned