code: public function modifySubmitedValueBeforeValidation($value, array $data) {
          if ($this->hasSubmittedValueModifier()) {
              return call_user_func($this->getSubmittedValueModifier(), $value, $data);
          } else {
              return $value;
          }
      }
docs: Modify incoming value before validating it. May be useful for situations when you need to clean
  incoming value from unnecessary data
  @param mixed $value
  @param array $data
  @return mixed