How does recursion work in PHP functions, and what are the practical considerations, such as stack depth limits, when writing a recursive function?

A recursive function is a function that calls itself, typically to solve a problem that can naturally be broken down into smaller instances of the same problem, such as traversing a nested directory structure or calculating a factorial, and while recursion can produce elegant, readable solutions, PHP has a practical limit on how deeply functions can call themselves before running out of available memory for the call stack, meaning very deep recursion on large datasets should generally be converted to an iterative loop based approach instead.

function factorial($n) {
    if ($n <= 1) return 1;
    return $n * factorial($n - 1);
}
echo factorial(5);