hooks class trying to understand them

Question

I built a small "hooks" class for adding some capabilities of basic plug-in functionality. Is it room for improvement?I am just beginng learning oop so don't be to harsh :D I got 2 method's for manually adding execution point's and deleting them, 1 autoloading method for plugins in a specific folder, and 1 method for execution. Sorry for any misspelling.Here's the code:

 defined('BASE_PATH') || (header("HTTP/1.1 403 Forbidden") & die('403 - Acces direct interzis.'));
class hooks
{
private  static $hooks = [];
private static $instance;

/**
 * @param null $plugin_dir
 * @return hooks
 * @desc ne asiguram ca avem o singura instanta globala
 */
public static function init($plugin_dir = null)
{
    if(self::$instance == null)
        self::$instance = new self($plugin_dir);
    return self::$instance;
}

/**
 * @param $plugin_dir
 * @desc instantierea efectiva, nu cred ca e nevoie de descriere si rulam load_action
 */
private function __construct($plugin_dir)
{
    self::load_action($plugin_dir);
}

/**
 * @desc ne aisguram ca obiectul nu poate fi clonat
 */
private function __clone(){}

/**
 * @param $plugin_dir
 * @return bool
 * @desc incarcarea dinamica de pluginuri (se efectueaza doar daca clasa este instantiata)
 * cautam directorul pt pluginuri le includem si le inregistram cu self::add_action
 */
private static function load_action($plugin_dir)
{
    if($plugin_dir == null)
        return null;
    $hooks = new GlobIterator($plugin_dir.DIRECTORY_SEPARATOR.'*.php', FilesystemIterator::KEY_AS_FILENAME);
    foreach($hooks as $hook => $file)
    {
        require_once $file;
        (empty($priority)) ? self::add_action($where, $callback) : self::add_action($where, $callback, $priority);
    }
    return null;
}

/**
 * @param $where punctul de executie
 * @param $callback metoda chemata poate fi functie sau metoda
 * @ex add_action('punct executie',[SomeClass, 'someStaticMethod']);
 * @param int $priority ordinea in care sant executate callbackurile pt fiecare pct de executie
 * @desc inregistram pluginuri
 */
public static function add_action($where, $callback, $priority = 50)
{
    if(!isset(self::$hooks[$where]))
        self::$hooks[$where] = [];
    self::$hooks[$where][$callback] = $priority;
}

/**
 * @param $where
 * @param $callback
 * @desc stergem un callback pt un pct de executie
 */
public static function remove_action($where, $callback)
{
    if(isset(self::$hooks[$where][$callback]))
        unset(self::$hooks[$where][$callback]);
}

/**
 * @param $where
 * @param array $args
 * @desc executam callbackurile pt un pct de executie si ai dam parametri necesari (optionali)
 */
public static function execute_action($where, $args = [])
{
    if(isset(self::$hooks[$where]) && is_array(self::$hooks[$where]))
    {
        arsort(self::$hooks[$where]);
        foreach(self::$hooks[$where] as $callback => &$priority)
            call_user_func_array($callback, $args);
    }
}

} index.php

define('BASE_PATH', realpath(__DIR__).DIRECTORY_SEPARATOR);
require_once BASE_PATH.'hooks.php';
hooks::init(BASE_PATH.'plugin'.DIRECTORY_SEPARATOR);
$array_pt_test = [
    'Home' => 'Home.php',
    'Top' => 'Top.php',
    'Hello' => 'Hello.php'
];
function render_nav($array =[])
{
    $output = '';
    foreach($array as $key => $value)
    {
        $output .= '<li>';
        $output .= '<a href="'.$value.'">'.$key.'</a>';
        $output .= '</li>';
    }
    echo $output;
}
hooks::add_action('nav', 'render_nav');

<nav id="nav">
                <ul>
                    <?php
                    hooks::execute_action('nav', [$array_pt_test]);
                    ?>
                </ul>
                <br class="clear" />
            </nav>

Simple exemple of displaying a nav menu. We register a default function (action) to process the array. In the overwrite.php(plugin folder) we register another function and give the overwrite_nav function a higher priority to be processed first and call the hooks::remove_action method to unregister the default one. Just play with the priority ($priority) value in overwrite.php to see the effect's. You can have multiple actions tied to the same execution point.

overwrite.php

 defined('BASE_PATH') || (header("HTTP/1.1 403 Forbidden") & die('403 - Acces direct interzis.'));
$where = 'nav';
$callback = 'overwrite_nav';
$priority = 57 ;

function overwrite_nav($array = [])
{
    hooks::remove_action('nav','render_nav');
        $output = '';
        foreach($array as $key => $value)
        {
            $output .= '<li>';
            $output .= '<a href="'.$value.'">'.strtolower($key).'</a>';
            $output .= '</li>';
        }
        echo $output;
}