In this example, the title of the page is set dynamically based on the page ID passed through the URL. The `getTitleFromDatabase` function retrieves the page title from a database using the `$page_id` variable. This would typically be used in a content management system or other dynamic web application. The `Page` class and `setTitle` function are not part of the standard PHP library, but are commonly included in web frameworks such as Laravel or CodeIgniter, or in custom libraries developed specifically for a particular web application.