135.1 Voting during a referendum shall be conducted in accordance with the Articles 104 and 105 of this Code.
135.2 A voter shall mark an empty square to the right of the answer on referendum ballot papers by choosing one of the responses “for” or “against” (“yes” or “no,” “I agree” or “I disagree”) proposed on the referendum.
135.3 If both squares are either marked or unmarked, the vote shall be considered invalid.