If it was really transparent maybe...

I would think that means that if the number of washing tablets went from 12 to 9, then packaging would display in prominent letters "Same price, now 9 tablets instead of 12"

Similarly for unit weights:

Chocolate biscuits, "same 12 biscuits, now 20g instead of 25g. Pack size reduced from 300g to 240g"

That would be transparency from my perspective.