I've always been really curious how this works - from what I remember back in my subversion days, both sides have things which are very hard to represent in one

I've always been really curious how this works - from what I remember back in my subversion days, both sides have things which are very hard to represent in one another. I imagine some of those are overcome by enforcing heuristics (e.g. the branches/tags/trunk hierarchy is mandatory and has business logic run based on it), but I'm really curious if there was ever a more detailed writeup on how it works?