OK, not intended for "everyday use"; I understand this as meaning that
it is considered primarily an internal interface, and thus one that has
an explicitly unstable API.  It is hard for me to guess that this would
be the case, since this intent is not documented in the docstrings or
comments of either TarFile.__init__() or TarFile.open()

If I'm understanding you correctly, this could be considered a
documentation bug; perhaps the docstring for TarFile.__init__() could
suggest using the open() method, except possibly within TarFile subclasses?

Sorry to be so confused here.  I hope I'm finally converging on
understanding...

Anyway, thanks for the help!