Thank you Jerome. Below is my code.

It behaves strangely. Hope you find my mistake.

//======== In start.php ==========
elgg_register_event_handler('init', 'system', 'title_menu_init');

function title_menu_init() {
    elgg_register_plugin_hook_handler('register', 'menu:title', 'title_menu_handler');
}

function title_menu_handler($hook, $type, $items, $params) {

     $unregister = array("groups:edit", "groups:invite", "edit:icon", "edit:cover");

     $owner = elgg_get_page_owner_entity();

      if($owner->type == 'group') {

            foreach ($items as $item) {

                 $item_name = $item->getName();

                 if (in_array($item_name, $unregister)) {

                      elgg_unregister_menu_item('title', $item_name);

                  } 

             }

            return $items;

       }

}

//======== In the view ========

$title_menu = elgg()->menus->getMenu('title', $params);// Trigger the hook

$title_menu = elgg()->menus->getMenu('title', $params);//== need to call twice to get the menu structure after triggering the hook

$sections = $title_menu->getSections();

$diff = count($sections,1) - count($sections,0);

if ($diff > 0) :

?>

<a class="title-button-nav" rel="toggle" data-toggle-selector=".title-menu-panel" href="#">

<?= elgg_view_icon('cog'); ?> 

</a>

<?php endif; ?>

<nav id="ram-title" class="title-menu-panel" role="navigation">

<?php echo elgg_view_menu('title', array('sort_by' => 'priority')); ?>

</nav>

Like i said in my earlier comment, you need to unset the item from $items like this:

foreach ($items as $index => $item) {

                 $item_name = $item->getName();

                 if (in_array($item_name, $unregister)) {

                      unset($items[$index]);

                  } 

             }

Don't call elgg_unregister_menu_item in the hooks they don't have any effect.

All is well that ends well

Now everything works well and makes sense.

Thank you very much Jerome for your help..... and patience :)

In the title menu there isn't necessarily an 'entity' in params, that's the error.

Also 'title' menu which is used by many plugins is not found in the developer tools

That's because in order to show information there we have to fake some menu's but the title menu has to many variables on order to fake correctly.

Lot's of menu items are dependent on page owner, context or something else.

I understand.

Thank you

Thank you iionly

Out of curiosity why do you use reference.elgg.org?

Since I setup Elgg in my IDE (Eclipse) I have autocomplete on all functions and I can click on a function to go to that function and read the documentation.

Before we had Eclipse setup correctly we used the reference extensively, but after the setup we never looked at it again.

This is very useful comment for me.

I'll start to learn and work with Eclipse IDE.

Thank you Jerome.

Thank you Jerome,

Yes, you are right. So far I found the username only in 2 cases: The Wire and a theme that I use, which I can handle.

However, exposing the username (e.g. in the URL) might be not the best security approach. 

In order not to cause massive problems in the internals of core and every plugin we thought about the following approach:

1. Add to  elggss_users_entity table a column "real_username" which includes the username. This column will be used during registration and login.
2. The username column will include a unique string (maybe some variation of the user GUID). It will be populated during registration.

In this way there is no need to change the plugins and the URL will include only the unique string, not the username. The only change should be done to the registration/login proccess.

What is your opinion?

Thank you

However, exposing the username (e.g. in the URL) might be not the best security approach. 

Why? Because with this you already have half of the credentials required to login? Maybe, but lots of websites use this approach.

1. Add to  elggss_users_entity table a column "real_username" which includes the username. This column will be used during registration and login.
2. The username column will include a unique string (maybe some variation of the user GUID). It will be populated during registration.

What is your opinion?

Seams like a lot of work for little gain.

Thank you Jerome.