The special missings material that was added to the v4.0 blog post belongs in
its own post: that article is a release announcement for v4.0, not a teaching
piece. This reverts the blog change and publishes the content under /feed/.
The new post covers what SAS special missings are, how the SASjs Adapter
carries them between the browser and SAS, and how Data Controller's validation
rules treat them - NOTNULL passes, MINVAL fails, MAXVAL passes, and the regex
rules apply as they would to any other value.
The LinkedIn version of the copy, and the image prompt for the cover, are
recorded in a comment at the foot of the file.