California Code, Elections Code - ELEC § 9317

(a) When an argument in favor and an argument against a measure have been selected for publication in the voter information pamphlet the elections official responsible for conducting the election shall send copies of the argument in favor of the measure to the authors of the argument against the measure and copies of the arguments against the measure to the authors of the argument in favor. The authors may prepare and submit rebuttal arguments not exceeding 250 words, or may authorize in writing any other person or persons to prepare, submit, or sign the rebuttal argument. The rebuttal arguments shall be submitted to the elections official conducting the election no later than a date designated by the elections official.

(b) Rebuttal arguments shall be printed in the same manner as the direct arguments. Each rebuttal argument shall immediately follow the direct argument that it seeks to rebut and shall be titled “Rebuttal to Argument in Favor of Measure (or Proposition) ___,” or “Rebuttal to Argument Against Measure (or Proposition) ___,” the blank spaces being filled in only with the letter or number, if any, designating the measure. Words used in the title may not be counted when determining the length of any rebuttal argument.