A modification is a real-time change to a web page designed to personalize or otherwise improve the user experience of the website and to guide visitors to complete a conversion. You can also use modifications to collect usage data from the site. You can place a modification in basically any web page element, either appending or replacing the element content.
Figure: Modifications appending and replacing original page content (click to enlarge)
This guide introduces modifications, describes the process of creating and managing them, and shows you how to optimize them to improve the performance of your site.