We have to use rules and actions if you wish to limit the number of modifiers you are able to select for a product (i.e only 3 sandwich fillings out of a possible 6).
The issue I have found that you are able to use a rule to remove last modifier if more than 3 are selected but this does not stop you selecting and already selected modifier more than once. (For example fillings Cheese, Tomato, Lettuce, Onion, Ham, Chicken. If you select Cheese, Tomato and Onion, you cannot select Ham, Chicken and Lettuce but you can still select multiples of Cheese, Tomato and Onion).
Iam not sure if this is intended behavior, if it is then you need to create a further rule for each modifier so that the last one is removed if it is selected more than once to stop this behavior from occurring.
My chef picked this up on a kitchen ticket today which stated that fillings where Tomato x 3, Onion and Ham and was confused !!
Does Multiple Selection mean being able to select more than one modifier in a group or being able to select a modifier more than once ?