function datum_leapyear( year )
	{
	 	if(((year % 4)==0) && ((year % 100)!=0) || ((year % 400) == 0))
      		return true;
   		else
	   		return false;
	}

	function datum_changeDays( target )
	{
		var dagen=new Array(13);
					
		dagen[0]=0; // wordt niet gebruikt
		dagen[1]=31;
		dagen[2]=28;
		dagen[3]=31;
		dagen[4]=30;
		dagen[5]=31;
		dagen[6]=30;
		dagen[7]=31;
		dagen[8]=31;
		dagen[9]=30;
		dagen[10]=31;
		dagen[11]=30;
		dagen[12]=31;			
		
		var DayList = document.getElementById( target+"_day" )
		var dy = parseInt(DayList[DayList.selectedIndex].value,10);
		var mnth=parseInt(document.getElementById( target+"_month").value,10);
		var yr = document.getElementById( target+"_year").value
		var days
		var x
		
		DayList.length=1;
		
		if(document.getElementById( target+"_month").value=="")
		{
			return;
		}
		
		days=dagen[mnth];
		if ((mnth==2) && datum_leapyear(yr)) days++;
								
		for(x=0; x<=days; x++)
		{
			var Opt = new Option()
			
			if(x==0){
				Opt.text = " ";
				Opt.value = "";
			}
			else
			{
				if( x<10 )
				{
					Opt.text = "0"+x;
					Opt.value = "0"+x;
				}
				else
				{
					Opt.text = ""+x;
					Opt.value = ""+x;
				}
			}
			
			if( x==dy )Opt.selected = true;
			
			if ( (dy > days) && (x==days) ) Opt.selected=true;
			DayList[x] = Opt;
		}
	}
	
	function datum_updateYearBox( strCalId )
	{
		return;
	}