EDI X12标准 - 我在哪里可以找到这个定义？

I've got a project I took over from someone that requires data to be exported in the EDI X12 Standard (837P) format. Although I have been able to find some samples that are useful I haven't been able to find anything that defines what the possible "segments" are and what they mean. The previous developer has quite a bit of work done, but I have no way of knowing if it's correct.I've got a project I took over from someone tha