An IFrame is an inline frame within a web page which contains an inline document. The term 'Forever IFrame' is used to denote an inline frame which is implicitly declared as infinitely long. This property of such frames allow the server to continually populate it with data. As browsers render and execute scripts on a page incrementally, the pushed data can be manipulated by the client as it passes into the frame.

The Forever IFrame delivery mode is supported by Universal Messaging's JavaScript API and can be used in all browsers. In addition to Forever IFrame, WebSocket Delivery Mode and Comet LongPolling Delivery Mode delivery modes are supported.

A Universal Messaging JavaScript client can communicate with a server using the Forever IFrame delivery mode by specifying the following configuration when starting a session: