So my understanding is that a community created on a certain server (say lemmy.world), can be interacted with by any other federated server, and any interactions from those servers are synced to the original "true" community / server. How does it work if two servers both have a community with the same name? Each server is the owner of content created there, and then Lemmy is just merging the communities with identical names so posts from both appear under server.com/c/Music?
/c/Music on server A could have drastically different rules from /c/Music on server B, so there's potential for users on both to see posts that wouldn't be allowed on their server?
Lemmy is just merging the communities with identical names so posts from both appear under server.com/c/Music?
No, lemmy doesn't merge communities from different servers, they're still different communities even if they have the same name (they actually don't since their server name is part of the community name).
Think of it as different subreddits.
While on reddit you can't have different subs with exactly the same name, there are still examples of same communities (that is subs dedicated to the same argument) with slightly different names, often spin-off of the original sub for various reasons.
They're different subs with different people and different mods, if you want to see them all, it's you who has to sub to all, not the server doing the merging for you.
some.lemmy/c/music is the music community on some.lemmy, if you want to see the music community on another.lemmy while you are at some.lemmy, you go to some.lemmy/c/music@another.lemmy
I'm still learning all this stuff too, so anybody please correct me if I'm wrong here, but to my understanding: They just exist alongside each other. They might locally have the same name but they'd have different URLs with the @[instance] suffix.
In your case, since you're a lemmy.world account, if you wanted to go to "music" communities, you'd navigate to:
lemmy.world/c/Music (this will take you to the "Music" community on lemmy.world)
lemmy.world/c/Music@lemmy.ml (this will take you to lemmy.ml's music community)
Communities with the same name across different instances are not merged, and the way they are referenced will be different. So, the location of lemmy.world/c/Music can also be referenced as !music@lemmy.world while instead the Music at serverB.whatever be can be referenced as music@serverB.whatever .
So when I see posts from a @someUser@some-server.com in lemmy.world/c/music, they had to visit lemmy.world and create a post in the music community here?
No, the point of federation is that you can interact with other sites/servers from your own since the same protocol is shared. So from some-server.com they visited music@lemmy.world and did their interaction. The same way you can go to the Music community at lemmy.ml ( https://lemmy.world/c/music@lemmy.ml ) without leaving lemmy.world and without having to create a new account. Your comments and interaction will be seen without problems by users of lemmy.ml .