code: func RegisterDriver(driver Driver) error {
  	if _, exists := drivers[driver.DbType]; exists {
  		str := fmt.Sprintf("driver %q is already registered",
  			driver.DbType)
  		return makeError(ErrDbTypeRegistered, str, nil)
  	}
  
  	drivers[driver.DbType] = &driver
  	return nil
  }
docs: // RegisterDriver adds a backend database driver to available interfaces.
  // ErrDbTypeRegistered will be returned if the database type for the driver has
  // already been registered.