Depends what form your talking about, do you mean the checkout form? Or do you have a contact form on the site? If so I guess its a hosted form?
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I assume @SreckoM is talking about the shopify ones as per http://wiki.shopify.com/How_to_add_a_contact_form_to_your_shop and have been wondering the same thing. It states some fields are required and validated, I wondered about making our own custom fields required and validated.
Not sure this should be in the job board though...is it a job request?