CLI modifications

I’m interested on that part which is responsible for the CLI itself. Can somebody tell me, where the command syntax (set commands, command description, actions etc.) are stored and maybe which open source software originaly is managing that?

I expect it is not ConfD which is a commercial on device orchestration solution which is now owned by cisco.

This may be of help:

That looks good - I will check it out in detail.
Does somebody know, which process is responsible for the CLI? Or is it something like a shell?