Legal regulations for eBikes

Hey everyone!

Been thinking a lot lately about custom eBike builds, especially with all the cool motors and batteries available now. It's awesome to dream up a super powerful machine for tackling those steep local trails, but it also got me wondering about the legal side of things. If you're building a custom eBike from scratch, how do you ensure it stays within the legal Class 1, 2, or 3 regulations, especially regarding motor wattage and speed limits? Are there any specific components or build practices that could accidentally push a custom build into moped or motorcycle territory in your experience?