var gotoPos = 0;

function doScroll() {

    if (window.pageYOffset)             pos = window.pageYOffset;
    else if (document.documentElement)  pos = document.documentElement.scrollTop;
    else if (document.body)             pos = document.body.scrollTop;

    if (window.innerHeight) h = window.innerHeight;                                  // mozilla
    else if (document.documentElement) h = document.documentElement.offsetHeight;    // ie 6
    else h = document.body.clientHeight;                                             // ie 5

    // 170 bepaalt min hoogte tov onderbalk
    gotoPos = Math.max(  (h-320) + pos   ,  objSubvantop = document.getElementById("center").offsetHeight-10  ); 
    setNavPos(); 
}

function setNavPos() {
    objNav = document.getElementById("navigatie");
    curPos = objNav.offsetTop;

    if (curPos!=gotoPos) {
        curPos = curPos + ( ( gotoPos- curPos ) / Math.abs(gotoPos-curPos)) ;
        objNav.style.top= curPos + "px"; 
        window.setTimeout("setNavPos()",5);
    }        
}

function blocking(nr)
{
	 if (document.getElementById)
	{
		vista = (document.getElementById(nr).style.display == 'block') ? 'none' : 'block';
		document.getElementById(nr).style.display = vista;
	}
}