我已尝试添加自定义li 到我的wordpress标题菜单，使用functions.php. 这是我的密码function 文件

function register_header_menu() {
   register_nav_menu(\'header-menu\',__( \'Header Menu\' ));
}
add_action( \'init\', \'register_header_menu\' );

将新元素添加到标题菜单

function add_new_item($items, $args) {
   if( $args->theme_location == \'header-menu\' ){
    $items .= \'<li> <a>Show whatever</a></li>\';
}
    return $items;
}
add_filter(\'wp_nav_menu_items\', \'add_new_item\');

我正在使用以下代码将菜单添加到header.php

wp_nav_menu( array(
  \'theme_location\' => \'header-menu\',
  \'container\'    => \'ul\',
  \'menu_class\' => \'menu\',
) ); ?>

菜单在标题上可见，但我的新项目在菜单中不可见。我怎样才能修复它？

add_filter( string $tag, callable $function_to_add, int $priority = 10, int $accepted_args = 1 )

function add_new_item_to_menu( $items, $args ) {
    if ( \'header-menu\' == $args->theme_location ) {
        $items .= \'<li><a>Show whatever</a></li>\';
    }
    return $items;
}
add_filter( \'wp_nav_menu_items\', \'add_new_item_to_menu\', 10, 2 );