by Byakuren » Thu Jan 07, 2016 05:37
No code is sent, it'll send the parts of nodes and entities and things that are important for the client to display and predict things, and also GUIs. For example, changes in entity velocity/acceleration are sent to the client, so that the client can predict the position of them. The client also sends events to the server like tool use and formspec button clicks, but all the mod code runs on the server.
Every time a mod API is left undocumented, a koala dies.