> Huh, although, how does it do that without using Windows API?

without knowing anything, i am going to guess that they could either directly import the same code that the windows api uses (either via knowing where the implementation code resides and load that), or even statically link the library! After all, regedit doesn't need to obey cleanliness rules that other non-first-party programs would need to - presumably, because if those registry editing api/format changes, regedit would get updated along with it!