Hi,
What you need is a "multiple" option to the hidden widget that builds something like this as the output
input name="myvar" type="hidden" value="A"
input name="myvar" type="hidden" value="B"
etc...
This does not exist, but it should not be hard to implement. It would then work automatically you could set a datatype and validate it, etc.
The only thing I have seen done is to pass the list as the hidden value and to convert it with split for processing.
