Multiple invoices per PDF

Since recently the dutch tax authorities allow multiple suppliers to combine their invoices in in one document.
(see article 3.2.3.1 at https://zoek.officielebekendmakingen.nl/stcrt-2017-59187.pdf)
How would you approach this in UBL? I could create one UBL document per invoice on the aggregate document, but then it's not possible to give them the same filename as the PDF.

The question/requirement was recently raised on the UBL comment list, and the TC has opened a ticket to track the status:

https://lists.oasis-open.org/archives/ubl-comment/201803/msg00000.html

https://issues.oasis-open.org/browse/UBL-175

I think the important question, which the TC is trying to understand is: Is this a single document that includes a collection of invoices issued by a number of suppliers, or is it a single document issued on behalf of all suppliers and which replaces the need for the suppliers to issue separate invoices?

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