[seL4] IPC

Searching on the sel4 repository, I find there is a manual talking about IPC (https://github.com/seL4/seL4/blob/9dba8e67ccb54e207bbec22e25f21c65e5c6a45f/m...) In addition to this material, where - particularly source code - would be a good start point to look into IPC design and implementation? Thanks