Expressions are used by Trackarr to determine which releases should be sent to a PVR.
A single release can be sent to multiple PVR's, provided it meets their associated filters.
This is achieved using the expr module by [antonmedv](https://github.com/antonmedv/expr), the language definition can be found [here](https://github.com/antonmedv/expr/blob/master/docs/Language-Definition.md).
