function unlimitedForLevel($categories, $parent_id = 0, $level = 0) { $results = array(); foreach ($categories as $category) { if ($category->parent_id == $parent_id) { $category->level = $level; $results[] = $category; $results = array_merge($results, unlimitedForLevel($categories, $category->id, $level + 1)); } } return $results; }In this example, we have a function called `unlimitedForLevel` that takes an array of categories as the first parameter, an optional parent ID as the second parameter (defaulting to 0), and an optional level as the third parameter (also defaulting to 0). The function then recursively loops through the categories and adds each one to the `$results` array if it matches the parent ID. It also sets the level property of the category object to the current level and merges any subcategories found using the `array_merge` function. This code example is likely to be found in a package or library related to e-commerce or content management systems.