Field usage of AS2 Multiple Attachments

I am implementing a service that can deliver multiple attachments in single AS2 message. Can somebody with experiences in industry advise that how to determine primary business payload among all attached payloads in an AS2 message. Is it the first payload or root part (AS2 multiple attachments is multipart/related structure - rfc6362 )primary ?

Also, does anybody know any usage of content-id and content-location headers in AS2 multiple attachments Are those headers commonly used in AS2 MAs? if they are, how they are used?( I knew single AS2 attachment doesn't use them, only the AS2 MAs is new to me)?




in our experience it is not a good practice to use multiple attachments. The reason is mainly not technical. If you attach more than a single EDI file to a transaction and would like to refer a single EDI file of this transaction you are running into problems. Normally the message tracking relies on the message id ( you are contacting your partner and tell him that the transaction with message ID "abc" contains data that is in wrong format, uses wrong qualifiers, has to be ignored etc) but how would you refer a single EDI file in the processing if there are lets say 10 messages with the same message id and a single one should be invalid?