UN/CEFACT e-CMR standard is hard to use. It is the same as all the rest. It is a throwback to the time when such things were intended for the techie elite. You enter into a parallel reality of CCL, RAM, UDT, RDM, XSD element maze and enumeration jungle. It is not a world for the uninitiated or fainted hearted - set aside weeks not days if you want to get to grips.
Is it worth it? Yes.