$source = [10, 20, 30, 40, 50, 60, 70];
$target = [1, 2, 3, 4];
// Insert elements from index 2 to 4 (30, 40, 50) into $target at position 1
$rangeToInsert = array_slice($source, 2, 3);
array_splice($target, 1, 0, $rangeToInsert);
print_r($target);
/*
run:
Array
(
[0] => 1
[1] => 30
[2] => 40
[3] => 50
[4] => 2
[5] => 3
[6] => 4
)
*/