inject.php

// Inject partials into main menu
add_filter('wp_nav_menu_items', function ($items, $args) {
    if ($args->menu->name != 'Primary') {
        return $items;
    }

    $dom = new DOMDocument();
    $dom->loadHTML($items);
    $xpath = new DOMXpath($dom);
    $find = $xpath->query('//li[contains(@class, "product-menu")]|//li[contains(@class, "resource-menu")]');

    $products = $dom->createDocumentFragment();
    $products->appendXml(silencio_partial('partials/product-sub-menu', [], false));

    $resources = $dom->createDocumentFragment();
    $resources->appendXml(silencio_partial('partials/resources-sub-menu', [], false));

    foreach ($find as $item) {
        $class = $item->getAttribute('class');

        if (stripos($class, 'product-menu') !== false) {
            $item->appendChild($products);
        } else if (stripos($class, 'resource-menu') !== false) {
            $item->appendChild($resources);
        }
    }

    return $dom->saveHTML();
}, 10, 2);