How is WordPress navigation menu implemented?

Question

PHP

I need the essence of the implementation, I want to do something similar
While I'm stuck on this code:
It's not clear how to nest a child menu, and how to close tags.
$nav_menuA = array(
array('id' => 12, 'item_parent' => 0, 'name' => 'primary_page', 'page' => 'primary_index.php'),
array('id' => 15 , 'item_parent' => 12, 'name' => 'page1', 'page' => 'index1.php'),
array('id' => 19, 'item_parent' => 0, 'name' => 'page4', 'page' => 'index4.php'),
);
$default = array('items' => '[ul class="
foreach($nav_menuA as $key => $item){
$sorted_menu_items[$key] = $item;
if($item['item_parent'])
$menu_items_with_children[ $item['item_parent'] ] = true;
}
if ( $menu_items_with_children ) {
foreach ( $sorted_menu_items as &$item ) {
if( isset( $menu_items_with_children[ $item['id'] ] ) ){
$output .= "[li][ul class=\"sub -menu\"]{$item['name']}[/ul][/li]";
}else{
$output .= '[li]'.$item['name'];
}
}
}
echo sprintf($format, $output);

Answer 1

If you really need the essence, then you need to read the WordPress code. On the other hand, if there are standard solutions in the form of wp_nav_menu() , why invent a bicycle... Read wp-kama.ru/function/wp_nav_menu there are also excerpts from the code.

Answer 2

https://gist.github.com/hitautodestruct/4345363 this code helped me many times.
I just remade it for myself, or, you can look in the direction of the Walker Menu.