A feature request follows.

Given we now have preprocessing function(value) in JavaScript, may it be possible one day to add secondary items to these?

I mean, function is called like function(value), but maybe it can be called like function(value, item2_value, item3_value, ...) with additional source items defined per preprocessing step. Of course, called only on 'master' item change, tracking of secondary items may be even desirable but would be too complex.

This would allow to effectively combine data from multiple item data sources and create complex checks / discoveries for cases where full dataset is not available from a single source.