Three-Dimensional Array in PHP

Here is an example of a three-dimensional array:

php<?php
  $arr = [
    [
      ['a', 'b'],
      ['c', 'd'],
    ],
    [
      ['e', 'f'],
      ['g', 'h'],
    ],
    [
      ['i', 'j'],
      ['k', 'l'],
    ],
  ];
?>

To output elements from such an array, it is already necessary to write three square brackets:

php<?php
  echo $arr[0][0][0]; // outputs 'a'
  echo $arr[2][1][0]; // outputs 'k'
?>

php<?php
  $arr = [
    [
      [1, 2],
      [3, 4],
    ],
    [
      [5, 6],
      [7, 8],
    ],
  ];
?>