Question regarding document copy and attachment in UBL

Good evening.

This is my first post to the UBL mailing list. I must also say that I'm not
yet very proficient with UBL, at all.

I'm working on a project that is using UBL 2.0 to represent invoices.
However, just yesterday, we've been trying to figure out how can we solve to
business problems. I'm pretty sure that they are, in one way or another,
contemplated in the UBL standard. I'm guessing it's more a question of
figuring how to get it done. The issues that we are trying to solve are as
follows:

#1 Scenario: A supplier issues an UBL 2.0 invoice but wants to send some
support documents along with it.
The first question that I ask is if I can send them inside the UBL? Can this
be done using the Attached Document?

#2 Scenario: The receiver of the invoice asks its supplier to resend the
invoice.
From what I've managed to find this can be done by marking the document as a
copy. Is there anything else that needs to be done to state that the
document is being resent?

Thanks in advance.

Best regards,
Diogo Almeida