function gradient(id, level)
{
	var box = document.getElementById(id);
	box.style.opacity = level;
	box.style.MozOpacity = level;
	box.style.KhtmlOpacity = level;
	box.style.filter = "alpha(opacity=" + level+ ")";
	box.style.display="block";
	return;
}


function fadein(id) 
{
	var level = 0;
	while(level <= 1)
	{
		setTimeout( "gradient('" + id + "'," + level + ")", (level* 1000) + 10);
		level += 0.01;
	}
}


// Open the lightbox

function openbox(formtitle, fadin)
{
  var box = document.getElementById('box'); 
  document.getElementById('filter').style.display='block';
  
  var btitle = document.getElementById('boxtitle');
  btitle.innerHTML = formtitle;
  
  if(fadin)
  {
	 gradient("box", 0);
	 fadein("box");
  }
  else
  { 	
    box.style.display='block';
  }  	
}	

// Close the lightbox

function closebox()
{
   document.getElementById('box').style.display='none';
   document.getElementById('filter').style.display='none';
}

// check email adres op formulier

        function check_email(email_id,err_id){
            emailRegExp = /^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.([a-z]){2,4})$/;
            var err_mail='Email adres ongeldig!';
            if(emailRegExp.test(document.getElementById(email_id).value)){
                //alert('true');
                return true;
            }else{
                document.getElementById(err_id).innerHTML=err_mail;
                alert(err_mail);
                return false;
            }
        }