WebPage Editor is a web-based interface for AEM authors & other business users to try out different content variations on published pages without opening Author instance.

Offer content change test to readers using this app is similar to having author instance available. By making this test, you can view how your content will look if text overflows, images moves, or font styles change. 

The changes made are applied to the page at next page refresh and you can try them out for a limited amount of time.

The offline app is an official application for Chrome browser and is designed to work offline. If the page you are working on requires online data, you will be unable to edit pages.