code: public static function multipleOf($base, $message = null)
      {
          if ($message === null) {
              $message = "Value must be multiple of $base";
          }
  
          // TODO: [PSI] create a predicate IsMultipleOf in the psi library
          $predicate = function ($value) use ($base) {
              /** @noinspection UnnecessaryCastingInspection */
              return fmod((float) $value, (float) $base) === (float) 0.0;
          };
  
          return new ResultsIn\OutcomeRule($predicate, $message);
      }
docs: @param float       $base
  @param string|null $message
  
  @return ResultsIn\OutcomeRule