text: """Validation errors."""
  
  
  class ConfigurationError(Exception):
      """Generic configuration error."""
  
  
  class MissingRequiredKeyError(ConfigurationError):
      """Missing required key error.
  
      Raised when a key that is described as required is not found.
      """
  
  
  class MissingDependencyError(ConfigurationError):
      """Missing dependency error."""
  
  
  class ValidationError(ConfigurationError):
      """Validation error."""
  
  
  class KeyDeclarationError(ConfigurationError):
      """Key declaration error."""
  
  
  class UnknownKeyError(ConfigurationError):
      """Unknown key error."""
  
  
  class DefaultValidatorError(ConfigurationError):
      """Default validator error."""
  