What is the difference between using $_marker[$i] and $_marker[] in PHP arrays?

Using $_marker[$i] in PHP arrays allows you to specify a specific index $i where you want to store a value in the array. On the other hand, using $_marker[] automatically appends the value to the end of the array without specifying an index. If you want to control the index where a value is stored in the array, you should use $_marker[$i]. If you simply want to add a value to the end of the array, you can use $_marker[].

// Using $_marker[$i] to specify index
$_marker = [];
$_marker[0] = "First value";
$_marker[1] = "Second value";

// Using $_marker[] to append values to the end
$_marker = [];
$_marker[] = "First value";
$_marker[] = "Second value";