%ERRORLEVEL% is an environment variable definie automatically by Dos9 at end of command runing. It enables checking if the previous command failed. With most commands, if %ERRORLEVEL% is equal to 0, then no error as occured.
The value of %ERRORLEVEL% makes no sense because any command is able to set its own %ERRORLEVEL% return values. Thus you should just consider if %ERRORLEVEL% is null to determine if errors have occured.
In a general way, signification of error codes in %ERRORLEVEL% is not important as long as most commands print an error message on failure.
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