Legal regulations for eBikes

Hey everyone!

Been thinking a lot about custom eBike builds lately, especially with all the cool motors and batteries out there. It's awesome to see what people are putting together, but it also got me wondering about the legal side of things. If you're building a custom eMTB or even a commuter from scratch, how do you ensure it still falls within the legal Class 1, 2, or 3 regulations, especially regarding motor wattage and top speed? Are there specific components or configurations that automatically push a custom build into a different, more regulated category, like a moped? Would love to hear your experiences or insights on navigating this!