What are potential pitfalls to be aware of when working with arrays in PHP?

One potential pitfall when working with arrays in PHP is accidentally overwriting existing array elements when using the assignment operator "=". To avoid this issue, use the array union operator (+=) to merge arrays without overwriting existing elements.

// Incorrect way: overwriting existing array elements
$array1 = [1, 2, 3];
$array2 = [4, 5, 6];
$array1 = $array2; // $array1 now contains [4, 5, 6]

// Correct way: merging arrays without overwriting
$array1 = [1, 2, 3];
$array2 = [4, 5, 6];
$array1 += $array2; // $array1 now contains [1, 2, 3, 4, 5, 6]