flattening array explanation

$array = [
    ['a', 'b'],
    ['c', ['d','e']],
    'f',
    ['g']
];

$flat_array = [];
flattening_array($array, $flat_array);

    // 1st iteration
    $item = ['a','b']
    is_array($item) // true
    flattening_array($item,$flattened)

        // 1st iteration
        $item = 'a'
        is_array($item) // false
        $flattened[] = $item // $flattened = ['a']

        // 2nd iteration
        $item = 'b'
        is_array($item) // false
        $flattened[] = $item // $flattened = ['a','b']

    continue // $flattened[] = ['a','b'] لكي لا ننفذ

    // 2nd iteration
    $item = ['c', ['d','e']]
    is_array($item) // true
    flattening_array($item,$flattened)

        // 1st iteration
        $item = 'c'
        is_array($item) // false
        $flattened[] = $item // $flattened = ['a','b','c']

        // 2nd iteration
        $item = ['d','e']
        is_array($item) // true
        flattening_array($item,$flattened)

            //1st iteration
            $item = 'd'
            is_array($item) // false
            $flattened[] = $item // $flattened = ['a','b','c','d']

            // 2nd iteration
            $item = 'e'
            is_array($item) // false
            $flattened[] = $item // $flattened = ['a','b','c','d','e']

        continue

    // 3th iteration
    $item = 'f'
    is_array($item) // false
    $flattened[] = $item // $flattened = ['a','b','c','d','e','f']

    continue

    // 4th iteration
    $item = ['g']
    is_array($item) // true
    flattening_array($item,$flattened)

        // 1st iteration
        $item = 'g'
        is_array($item) // false
        $flattened[] = $item // $flattened = ['a','b','c','d','e','f','g']

    continue

//  في النهاية سنجد ان
//  $flat_array = ['a','b','c','d','e','f','g'];
//  لاننا قمنا بتمرير بالاشارة