old_contents: /**
   * Farts.
   *
   * @param {boolean=} opt_isWet Whether the fart is wet.
   */
  function fart(opt_isWet) {
    if (opt_isWet) {
      console.log('pfffffpfpfpffffff?');
    } else {
      console.log('poooOOOot.');
    }
  }
  
new_contents: /**
   * Farts.
   *
   * @param {boolean=} opt_isWet Whether the fart is wet. (Optional)
   */
  function fart(opt_isWet) {
    if (opt_isWet) {
      console.log('pfffffpfpfpffffff?');
    } else {
      console.log('poooOOOot.');
    }
  }
  
subject: Correct a glaring oversight in the documentation.