Web Design in a Nutshell, 3rd Edition

Providing alternate content

If the browser determines that it cannot render the specified object, it then proceeds to render the content of the object element. In the example from earlier in this section, should the browser not have the capacity to render the GIF, it will display the alternative content (“A color photograph of a daffodil”) instead.

<object data="daffodil.gif" type="image/gif" width="150" height="125">
A color photograph of a daffodil.
</object>

The alternative content may also be another object element. Authors may provide several layers of alternate content by nesting objects with different implementations. The user agent will keep looking inside each object element until it finds an object that it can render.

In this example, borrowed from the HTML 4.01 Recommendation, a Python applet is embedded on the page with the object element. If the browser can’t render the applet, an MPEG video is provided as a backup. If the video cannot be rendered, there is a static GIF image, and finally, a text description is provided if all else fails.

<object title="The Earth as seen from space" classid="http://www.observer.
mars/TheEarth.py">
    <object data="TheEarth.mpeg" type="application/mpeg">
        <object data="TheEarth.gif" type="image/gif">
              The Earth as seen from space.
        </object>
    </object>
</object>