What does this array construct in php do?

Question

PHP

Give an illustrative example of array constructions in php. In particular, I am interested in what I will get from this type of array:
$arr[$item[$subItem]] [$num]
Please tell me what this moment means in this code: [$item[$subItem]] ?
ps Variable names are random.

Answer 1

This is a two dimensional array. If $num or $item[$subItem] contains a string, the array is associative, meaning the string is the key, not the number(0,1,2). This is a one dimensional array.
$item[$subItem]