What is the meaning of -a option in tar.exe command?

tar(1):

...
-a, --auto-compress
             (c mode only) Use the archive suffix to decide a set of the
             format and the compressions.  As a simple example,
                   tar -a -cf archive.tgz source.c source.h
             creates a new archive with restricted pax format and gzip
             compression,
                   tar -a -cf archive.tar.bz2.uu source.c source.h
             creates a new archive with restricted pax format and bzip2
             compression and uuencode compression,
                   tar -a -cf archive.zip source.c source.h
             creates a new archive with zip format,
                   tar -a -jcf archive.tgz source.c source.h
             ignores the "-j" option, and creates a new archive with
             restricted pax format and gzip compression,
                   tar -a -jcf archive.xxx source.c source.h
             if it is unknown suffix or no suffix, creates a new archive with
             restricted pax format and bzip2 compression.
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