var level1DOMsupported = document.createElement;

window.onload = checkDisplayGoToTopButton;
window.onresize = checkDisplayGoToTopButton;

function checkDisplayGoToTopButton()
{
	if ( ! level1DOMsupported ) { return; }
	var elem = document.getElementById ( 'sluitregel' );
	if ( ! elem ) { return; }
	
	var windowHeight = document.documentElement.clientHeight || document.body.clientWidth;
	var beleg = document.getElementById('beleg');
	var posSluitregel = beleg.scrollHeight + beleg.offsetTop;
	
	if ( posSluitregel > windowHeight )
	{
		elem.style.display = "block";
		elem.onclick = function ( )
		{
			scrollTo ( 0, 0 );
		}
	}
	else
	{
		elem.style.display = "none";
	}		
}