Constrain Found Set can be performed both manually or via script. If you search the script steps in the Script editor you'll find a step with that name.
Just keep in mind what Constrain Found Set really does.
Constrain Found set works just like Perform Find except:
Perform find searches the entire table for records matching the search criteria.
Constrain Found set searches only the current found set.
Thus if my table contains all company sales people nation wide, and I perform a find for all Salespersonnel living in California...
Entering find mode, specifying "left handed"...
Perform Find at this point finds all lefthanded salespersonnel nationwide.
Constrain Found set would find all California Salespersonnel that are left handed.
I had investigated the script step you mention. Yet it seems that ultimately the *criteria* must be entered. Am I wrong? The criterion(a) is what I would like to let the user select, not have to enter.
Yes, of course it does :)
Thank you, comment.