[JdeBP]

Originally it was echo -n, local, and logical operators in test. There was just so much Debian stuff that assumed these.

* https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=294962

They've added 2 more since.

* https://www.debian.org/doc/debian-policy/ch-files.html#scrip...

Strictly speaking, there are other differences between the Debian Almquist shell and a truly SUS conformant sh.

* https://unix.stackexchange.com/q/697007/5132

But the aforementioned are what Debian people explicitly wanted and couldn't live without. Note that the StackExchange answer is a comparison of a 2022 dash to a 2017 standard, neither of which existed at the time. Debian Policy, the Debian Almquist shell, and the POSIX standard have all been revised since then.