$1 is simply a placeholder for the field being processed. In your posted example, all fields tagged with '$date' will get processed. If the current field is 'OrderDate', the $1 gets substituted in the script and you have:
Year(OrderDate) As Year tagged '$year'
No, it does not make sense in this example to ever use $2.
Thanks Rob! That makes it clear. What about Question 1? I know I could find some potential scenarios, but out of curiosity 🙂 - have you ever applied this method to create some derived dimensions other than dates ?
ex-Training Manager at Qlik Central-Eastern Europe