Any URL on a screen: how it is rendered, the settings that control it, sending screen details to the page, and pages behind a login.
If it has a URL, it can go on a screen. The device opens it in a full-screen browser with no tabs, no address bar, and nothing to click.
Web pages cover the most ground of any content type, and carry the most settings, because a page written for a person at a laptop is not automatically right on a wall.
How a page is rendered, where it is rendered, what it needs to do to display at all, and how pages on your own network work.
A page reloads each time it comes round in the playlist. When that is not enough, and when forcing a refresh makes things worse.
Turn on Send metadata and the player identifies itself in HTTP headers, so one URL can show different content per location.
Three ways to show a page that needs authentication: the browser extension, JavaScript injection, and client certificates for enterprise networks.