Question about role-based images

In the Stayton book in the section on SVG in HTML, there is an example 
of using an SVG graphic for PDF and PNG for HTML. I tried it and it 
didn't work.

This is the XML I used:

  <mediaobject>
             <imageobject role="fo">
                 <imagedata format="SVG" scale="75" 
fileref="Graphics/network-topology_one-subnet.svg" align="center" 
scalefit="1"/></imageobject>
                 <imageobject role="html">
                  <imagedata format="PNG" scale="75" 
fileref="Graphics/network-topology_one-subnet.png" align="center" 
scalefit="1"/></imageobject>
         </mediaobject>


The HTML is:

<div class="mediaobject" align="center"><img 
src="Graphics/network-topology_one-subnet.svg" width="405" align="middle">

Version info for XSLTproc:

Using libxml 20706, libxslt 10126 and libexslt 815
xsltproc was compiled against libxml 20706, libxslt 10126 and libexslt 815
libxslt 10126 was compiled against libxml 20706
libexslt 815 was compiled against libxml 20706

Solution?
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Steve Johnson, Senior Content Developer
Caringo