<script for="c" event="onclick">
if (event.srcElement.m=='')
for(var i=1;i<c.length;i++)
c[i].checked=c[0].checked;
else{
var tmp1 = true, tmp2 = false
for(var i=1;i<c.length;i++)
tmp1 &= c[i].checked, tmp2 |= c[i].checked;
c[0].checked = tmp1;
c[0].indeterminate = !tmp1 && tmp2;
}
</script>
<table border>
<tr><td><input type="checkbox" name="c" m></td></tr>
<tr><td><input type="checkbox" name="c"></td></tr>
<tr><td><input type="checkbox" name="c"></td></tr>
<tr><td><input type="checkbox" name="c"></td></tr>
<tr><td><input type="checkbox" name="c"></td></tr>
</table>