1<?xml version="1.0" standalone="yes"?>
2<smil>
3  <body>
4<!-- The SMIL <switch> element will process the
5         first child element which tests true and skip
6         past all others. -->
7    <switch>
8<!-- The system-required attribute tests to see if
9           the user agent supports SVG. If true, then
10           render the file drawing.svg. -->
11      <ref system-required="http://www.w3.org/Graphics/SVG/svg-19990412.dtd" type="image/svg" src="drawing.svg"/>
12<!-- Else, render the alternate image. -->
13      <img src="alternate_image.jpg"/>
14    </switch>
15  </body>
16</smil>
17