In

https://stackoverflow.com/questions/69108632/unable-to-catch-exception-error-for-argparse

it looked like `exit_on_error` does not work when using subparsers.  On on further thought, I realized that it has to included in the definition of the subparser.  As with other `ArgumentParser` parameters, the subparsers does not inherit from the main parser.  

So it's basically a documentation issue.  The `add_parser` method is described briefly as:

     which takes a command name and any ArgumentParser constructor 
     arguments, and returns an ArgumentParser object that can be 
     modified as usual.

But as my experience shows, its relevance is easily missed, even by an experienced users.