example
<par>
<a href="#Story"> <img src="button1.jpg"/> </a>
<a href="#Weather"> <img src="button2.jpg"/></a>
<excl>
<par id="Story" begin="0s">
<video src="video1.mpg"/>
<text src="captions.html"/>
</par>
<par id="Weather">
<img src="weather.jpg"/>
<audio src="weather-rpt.mp3"/>
</par>
</excl>
</par>
