Give access to properties of the entity being updated in the upsert by allowing .entity notation or similar

Would allow counters to be incremented when an event takes place e.g. {{ .entity.properties.counter + 1 }}

If title or string property needed to contain string from most recent updated related entity would be able to separate out the current string e.g. {{ .entity.properties.name | split(" ") | .[0] + .event.context.entityIdentifier }}