You may also be interested in the docs for these other parts of Starknet.
Nethermind's Starknet full node implementation is called Juno. Juno has its own documentation. It's open source and running a full node is permissionless on Starknet.
Starknet RPC Spec
The specification for the Starknet RPC API is maintained by Starknet and implemented by the full node teams.