These two are by far and away the most popular, having millions of copies installed. A SMIL document's structure is similar to the HTML document structure. As with HTML, each visual object in SMIL occupies a certain area of the browser's viewport, or display area. Thus, a SMIL browser's display area is divided into regions. Each region contains a media document such as streaming video, text, an image, etc.
Any visual object is contained in a region.
This ID is used as a reference to this region in the rest of the document. Rendering of different components can occur either sequentially or in parallel. This snippet instructs the SMIL interpreter to render two images simultaneously. This reflects the fact that a region may have different contents at different moments. The end attribute indicates when the elements should be no longer displayed.