slides in XML
<document>
...
<slide id="1">
<text>
<line>What about the slide format?</line>
<break/>
<line>yeh, what about it"?</line>
</text>
<vrml>Sphere { radius 0.5 }</vrml>
</slide>
...
<slide id="2">
<vrml>Sphere { radius 0.5 }</vrml>
</slide>
...
</document>
