I am really need your help.

I have a list with checkboxes, like:

CHK1(main category)

--CHK2(sub category)

--CHK3(sub category)

--CHK4(sub category)

How can I do the next things:

1) When I click the CHK1 all sub categories will checked?

2) When I check the sub category, the main category will checked automatic?

THANKS.