Has anyone considered extending dash?

Thanks, that's good to know. (Looking at it, I believe I might have erroneously used pushd/popd myself.)

However, it appears to be a list of generic features, so it's far from a thorough list. While the "Bash POSIX Mode" subsection goes into more detail, I didn't see any mention of, for example, bash-specific expansion patterns like ${foo/bar/baz}.

> Every time I have a doubt about standard conformance I just google for "opengroup + sh-keyword"

Unfortunately, bash (like Perl) has gobs of Google-unfriendly concepts. (Searching the standard for "." was fun...)