function veil(obj) {
	setVeilVisibility(getFirstChildByName(obj, 'veil'), 'visible');
}

function unveil(obj) {
	setVeilVisibility(getFirstChildByName(obj, 'veil'), 'hidden');
}

function setVeilVisibility(veil, vis) {
	if(veil)
		veil.style.visibility = vis;
}

function getFirstChildByName(obj, name) {
	var kids = obj.childNodes;
	for(var i=0; i<kids.length; i++) {
		if(kids[i].nodeType == 1 && kids[i].getAttribute('name') == name)
			return kids[i];
	}
	return false;
}

function setHeading(txt) {
	document.getElementById('body_text').innerHTML = '<h1>' + txt + '</h1>';	
}

function hideNav() {
	document.getElementById('preview_nav_left').style.visibility = 'hidden';
	document.getElementById('preview_nav_right').style.visibility = 'hidden';
}

// variables to control scroll behaviour
var scrollInt=0;
var scrollSpeed=30;
var scrollLength=10;

// continually scroll up
function scrollLeft_() {scrollInt = setInterval("scrl(scrollLength)", scrollSpeed);}

// continually scroll down
function scrollRight_() {scrollInt = setInterval("scrl(-scrollLength)", scrollSpeed);}

// stop scrolling
function scrollStop() {clearInterval(scrollInt);}

// scroll in given number of pixels
function scrl(px) {document.getElementById('scroller').scrollLeft -= px;}