how CDA files are being transported in HL7 messages or IHE_XDM.ZIP?

I am trying to understand how the Mediboard App has implemented CDA exchange (open source = https://gitlab.com/openxtrem_public/mediboard/-/tree/master) so as I read from the official documentation CDA are packaged inside Hl7 messages but I also read and found in the code that CDA is stored in IHE_XDM.ZIP using XDM, and then being transported
so which one is the right way?