[ic] IC 5.2 How to require a field when fieldname is variable

[Russell Mann]

Hello,

I have a system setup to handle gift subscriptions that can be sent to a
user input email address.  What I need to do is for the checkout form have a
field name like this:

emailto_[item-increment]

Be required, and be required as an email address.  But I only want it
required if the [item-increment] numbered item is one of these gift
products.

Any suggestions on how to add dynamically a field to the "required" list?

Thanks,

Russell Mann