yii\validators\BooleanValidator::validateValue PHP Method

    protected function validateValue($value)
    {
        $valid = !$this->strict && ($value == $this->trueValue || $value == $this->falseValue) || $this->strict && ($value === $this->trueValue || $value === $this->falseValue);
        if (!$valid) {
            return [$this->message, ['true' => $this->trueValue === true ? 'true' : $this->trueValue, 'false' => $this->falseValue === false ? 'false' : $this->falseValue]];
        }
        return null;
    }