[TYPO3-english] powermail: One of three fields mandatory

[Sebastian Michaelsen]

Hi,

I have three fields of type checkbox, each including several checkboxes. 
The user must choose at least one option of one of the fields.

A
[ ] A1
[ ] A2

B
[ ] B1
[x] B2

C
[ ] C1
[ ] C2
--> valid


Is this something I can achieve easily?

If not on serverside it is acceptible to implement this validation only 
on clientside. I could write a validation process to check the fields in 
Javascript (jQuery), but any idea how I can integrate my custom 
validation into the jQuery Tools validation (that is used by powermail)?

Thanks in advance for any help.

Kind regards,
Sebastian