is( $span.intersects( $span2 ), bool::true, 'intersects' );

is( $span.intersects( $span3 ), bool::false, 'doesn\'t intersect' );

is( $span.intersection( $span2 ).stringify, '[2,3]', 'intersection' );

is( $span.union( $span2 ).stringify, '[1,4]', 'union' );