eZ\Publish\Core\FieldType\Date\Type::validateFieldSettings PHP Method

    public function validateFieldSettings($fieldSettings)
    {
        $validationErrors = array();
        foreach ($fieldSettings as $name => $value) {
            if (!isset($this->settingsSchema[$name])) {
                $validationErrors[] = new ValidationError("Setting '%setting%' is unknown", null, array('%setting%' => $name), "[{$name}]");
                continue;
            }
            switch ($name) {
                case 'defaultType':
                    $definedTypes = array(self::DEFAULT_EMPTY, self::DEFAULT_CURRENT_DATE);
                    if (!in_array($value, $definedTypes, true)) {
                        $validationErrors[] = new ValidationError("Setting '%setting%' is of unknown type", null, array('%setting%' => $name), "[{$name}]");
                    }
                    break;
            }
        }
        return $validationErrors;
    }