actually work (but just happen to, today, and in some cases, even
that trusts to some luck.)
It has been recently pointed out to me that the man page (ie: this
file) doesn't give any real guidance to what is really acceptable,
and what is not.
The CAVEATS section does note that the grammar is ambiguous, but then
just says that test(1) implements what POSIX requires, and refers
readers to the relevant section of the POSIX standard for more details.
That is probably asking too much of the average reader...
So, add some extra information in the CAVEATS with what is defined to work,
and what should be avoided. Not all of the POSIX rules are here, but this
might hopefully help script authors avoid some of the pitfalls.