So far, the where clause only supported simple FilterFunction conditions.
With this, we want to add support for conditions where the an event is accepted not only based on its own properties, e.g. name, as it was before, but also based on some statistic computed over previously accepted events in the pattern, e.g. if the price is higher than the average of the prices of the previously accepted events.
This in combination with the recently added quantifiers will allow for a lot more expressive patterns.