function references()
{
	var selected = [];
	var selects = $$('select.document_type');

	for(var i = 0, count = selects.length; i < count; i++)
	{
		var select = selects[i];
		var value = select.options[select.selectedIndex].value;

		if(value != '-')
		{
			selected.push(value);
		}
	}

	var references = $$('div.reference');
	var showAll = (selected.length == 0);

	for(var i = 0, count = references.length; i < count; i++)
	{
		var reference = references[i];

		if(showAll)
		{
			reference.show();
		}
		else
		{
			var id = reference.id;
			var hide = false;
			id = id.split('_');

			for(var j = 0, count2 = selected.length; j < count2; j++)
			{
				if(id.indexOf(selected[j]) == -1)
				{
					hide = true;
					break;
				}
			}

			if(hide)
			{
				reference.hide();
			}
			else
			{
				reference.show();
			}
		}
	}
}