document.getElementsByClassName = function(clsName){
    var retVal = new Array();
    var elements = document.getElementsByTagName("*");
    for(var i = 0;i < elements.length;i++){
        if(elements[i].className.indexOf(" ") >= 0){
            var classes = elements[i].className.split(" ");
            for(var j = 0;j < classes.length;j++){
                if(classes[j] == clsName)
                    retVal.push(elements[i]);
            }
        }
        else if(elements[i].className == clsName)
            retVal.push(elements[i]);
    }
    return retVal;
}
function isIE6() {
  var isIE6 = false;
	try { // Firefox, Opera 8.0+, Safari, IE7
		xmlHttp=new XMLHttpRequest();
	} catch (e) {
		// Internet Explorer <7
		isIE6 = true;
	}
	return isIE6;
}

function validate() {
  var verplichte_velden = document.getElementsByClassName('verplicht_veld');
  for (t=0; t<verplichte_velden.length; t++) {
    if (!verplichte_velden[t].value || verplichte_velden[t].value == "") {
      alert ("Het veld '"+verplichte_velden[t].name+"' is verplicht.");
      verplichte_velden[t].focus();
      return false;
    }
  }
}

function highLight(iD) {
  document.getElementById(iD).style.backgroundColor = '#CCCCCC';
}
function lowLight(iD) {
  document.getElementById(iD).style.backgroundColor = '';
}