public static function array_multilevel (&$array, $name, $fn = null, $separator = '.') {
		$name_tree = explode($separator, $name);

		if (count($name_tree) > 1) {
			$name_tree = array_reverse($name_tree);
			$name = array_pop($name_tree);
			$name_tree = array_reverse($name_tree);
			$name_tree = implode($separator, $name_tree);

			if (!isset($array[$name]))
				$array[$name] = [];

			return static::array_multilevel ($array[$name], $name_tree, $fn, $separator);
		} else {
			$value = (isset($array[$name]) ? $array[$name] : null);

			// Functional getter

			if (!is_null($fn) && is_callable($fn)) {
				$result = $fn($value);

				// Setter

				if (!is_null($result))
					$array[$name] = $result;
			}

			return $array[$name];
		}
	}