externalErrorMessage property
A short explanation for the error, which can be shared outside Google.
Please set domain, code and arguments whenever possible instead of this error message so that external APIs can build safe error messages themselves. External messages built in a RoSy interface will most likely refer to information and concepts that are not available externally and should not be exposed. It is safer if external APIs can understand the errors and decide what the error message should look like.
Implementation
core.String? externalErrorMessage;