PHP: Can anyone explain that code?

Question

$letters = array ("a", "b", array("c", "d"), "e");
echo (count($letters, 1));

The output is 6, but why?
I know the count() function but don't know what the second parameter (in this case 1) does.
Can someone explain?

Answer 1

the 1 will probably be the position of element that should be printed

Answer 2

The second (optional) parameter is set to 1, so count() will count recursively.
https://www.php.net/manual/en/function.count.php

Answer 3

*AsterisK* position of an element of the array?