When you include your own JavaScript functions in a page or component, you have to take care that the formatting doesn't go awry. So I recommend you use the following approach (pay special attention to the comment tags at the start and end of the script tags):
<script type="text/javascript" language="JavaScript">
var myValue = '${prop:value}'; // before the comment so Tapestry sees it!
<!-- //
// Toggle the display of a set of elements between show and hide
function toggle() {
for ( var i=0; i < arguments.length; i++ ) {
$(arguments[i]).style.display = ($(arguments[i]).style.display != 'none' ? 'none' : '' );
}
}
// -->
</script>