Notice in the <head> section in code view, the JavaScript for the behaviour has been added, in this case:
<script type="text/javascript">
function FP_changeProp() {//v1.0
var args=arguments,d=document,i,j,id=args[0],o=FP_getObjectByID(id),s,ao,v,x;
d.$cpe=new Array(); if(o) for(i=2; i<args.length; i+=2) { v=args[i+1]; s="o";
ao=args[i].split("."); for(j=0; j<ao.length; j++) { s+="."+ao[j]; if(null==eval(s)) {
s=null; break; } } x=new Object; x.o=o; x.n=new Array(); x.v=new Array();
x.n[x.n.length]=s; eval("x.v[x.v.length]="+s); d.$cpe[d.$cpe.length]=x;
if(s) eval(s+"=v"); }
}
function FP_getObjectByID(id,o) {//v1.0
var c,el,els,f,m,n; if(!o)o=document; if(o.getElementById) el=o.getElementById(id);
else if(o.layers) c=o.layers; else if(o.all) el=o.all[id]; if(el) return el;
if(o.id==id || o.name==id) return o; if(o.childNodes) c=o.childNodes; if(c)
for(n=0; n<c.length; n++) { el=FP_getObjectByID(id,c[n]); if(el) return el; }
f=o.forms; if(f) for(n=0; n<f.length; n++) { els=f[n].elements;
for(m=0; m<els.length; m++){ el=FP_getObjectByID(id,els[n]); if(el) return el; } }
return null;
}
function FP_changePropRestore() {//v1.0
var d=document,x; if(d.$cpe) { for(i=0; i<d.$cpe.length; i++) { x=d.$cpe[i];
if(x.v=="") x.v=""; eval("x."+x.n+"=String(x.v)"); } d.$cpe=null; }
}
// -->
</script>