Multi-Select 0 and value?

I have a multi-select with:

0 - no limit
node_id to limit the use of a function
node_id to limit the use of a function
node_id to limit the use of a function

But a clever user can select none and 1, 2, and 3;
how can I avoid this?

Would it be better to use the opposite logic with 0 = all
so I don't have to care about what else is selected?


Nothing = no limit
0 = nothing = no limit
1,2,3 = limit to 1,2,3

but
0,1,2,3 = ?

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