Legal regulations for eBikes

Hey everyone!

Just finished a sweet DIY mid-drive conversion on my old mountain bike, and it's running like a dream. Now that I'm zipping around, it got me thinking about the legal side of things, especially with DIY builds. What are your experiences with local regulations for eBikes, particularly when you've modified them yourself? Are there specific power limits or speed cut-offs I should be aware of that might differ for a custom build versus a factory one? I'm in [mention your general area, e.g., "California" or "the UK"] if that helps, but interested in hearing from anywhere!