Learning Reflection thoroughly

I always wondered, how do the developers behind tools like StructureMap, AutoMapper, PostSharp, ORMs, frameworks etc know Reflection (and other technologies for sure, but i'm asking specifically on reflection) in such a high level. When I look for information on Reflection, i only find some superficial tutorials that teach only the basics of the basics. As far as I'm aware of, there are no books on the subject, only tutorials on the internet.
How do I learn the subject deeply?

thanks,
ashilon