They used to be ACLs in principle, but those were mainly replaced by simpler graph-based settings: Friends only, Public, being the two big ones. Personally, I u

They used to be ACLs in principle, but those were mainly replaced by simpler graph-based settings: Friends only, Public, being the two big ones. Personally, I used lists a lot (by language, interest, etc.: I had up to 50 actively used lists) and the idea of acquaintances (friends who you don’t let follow you, which is a very convenient abstraction also being phased out). The simplification had many justification (and some detractors, including me) but the key idea is that who has access to which posts is now more dependent on the graph structure than lists that too few people were maintaining. Typically, if you set a list and made friends who would fit in a list, you only add them later and there were some inconsistency around whether they should see your old posts. Most of the changes that I’ve noticed happened after I left, but the main motivation is: users don’t understand edge cases of ACLs (or NTFS) and they really hate being surprised. Either way, actually: acquaintances hate realising they couldn’t see their “friend’s” posts; new friends hate seeing their old posts becoming visible. The abstraction of a Group has clearly emerged as a much better way to give posts context: groups have moderators, rules, shared expectations. Those two are graph-based, rather than ACL, but the inconsistencies that you can imagine around changing membership make more sense to users. Where it’s really different is that it’s enforced at the language level: Facebook uses Hack, a custom version of PhP where all those concepts are abstracted into the language, to be absolutely sure that junior developers can’t mess up and give access to a un-authorised resources involuntarily, or be attacked because they didn’t know about a unusual type of injection. That’s why ACLs, although still technically available through some old interfaces, are being phased out: they don’t scale well in that context, in addition to their unexpected behaviour. I’d love someone to explain that better than I can, but I suspect it’s one of those tech that doesn’t make sense outside of the project, and that is possibly more secure if less people understand it well.