Matt Rickard has a good entry level blog post about it, from the angle of regex constraining [0]. Context free grammars follow the same principle, except using

Matt Rickard has a good entry level blog post about it, from the angle of regex constraining [0]. Context free grammars follow the same principle, except using a finite state machine to restrict the action space. [0]: https://matt-rickard.com/rellm https://matt-rickard.com/rellm