<script language="JavaScript" type="text/javascript">
var f = false;
function mark(field)
{
if(!f)
{
for(i=0;i<field.length;i++)
field[i].checked = true;
f = true;
}
else
{
for(i=0;i<field.length;i++)
field[i].checked = false;
f = false;
}
}
</script>