After adding all the headers and content to the page, you want to get the page to the user. display() directly echoes the page to the browser.
If you want to do something with the result page before pushing it to the browser, use toHtml() . It returns the page as string that can be modified further.
<?php //push it to the browser $page->display(); //or put it into a variable $html = $page->toHtml(); ?>