I'm very much at the beginning of using / understanding [EventStore](https://geteventstore.com/) or get-event-store as it may be known here.

I've consumed the documentation regarding clients, projections and subscriptions and feel ready to start using on some internal projects.

One thing I can't quite get past - is there a guide / set of recommendations to describe the difference between event metadata and data ? I'm aware of the notional differences; Event data is 'Core' to the domain, Meta data for describing, but it is becoming quite philisophical. 

I wonder if there are hard rules regarding implementation (querying etc). 

Any guidance at all gratefully received!