With the development of Universal Forms, we are including accepted file types, rule-based logic for required/not-required, maximum number of files, minimum number of files, and maximum file size. This should also include invalida characters.
If you have any other requirements, please let us know in the comments section below.
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We are currently working on our new Responsive designer which has an improved rules engine. This will allow you to conditionally require attachments.
I will update this ticket when we release the new Responsive designer.
EuanDario Cassinerio commented