@opendna @april @afoozle It’s called the ‘bundled’ option word.

“The first synopsis form shows a “bundled” option word. This usage is provided for compatibility with historical implementations. See COMPATIBILITY below for details.

The other synopsis forms show the preferred usage. The first option to tar is a mode
indicator from the following list:…”

…

“The bundled-arguments format is supported for compatibility with historic implementations.
It consists of an initial word (with no leading - character) in which each character indicates an option. Arguments follow as separate words. The order of the arguments must match the order of the corresponding characters in the bundled command word. For example,
tar tbf 32 file.tar
specifies three flags t, b, and f. The b and f flags both require arguments, so there must be two additional items on the command line. The 32 is the argument to the b flag, and file.tar is the argument to the f flag.

The mode options c, r, t, u, and x and the options b, f, l, m, o, v, and w comply with
SUSv2.

For maximum portability, scripts that invoke tar should use the bundled-argument format above, should limit themselves to the c, t, and x modes, and the b, f, m, v, and w options.”

https://manpages.ubuntu.com/manpages/bionic/man1/bsdtar.1.html