It would be nice to update the preceding comment, "For ISO format use:"

Maybe remove the comment entirely. The commented-out \newcommand is old, and with this proposed change the comment "For ISO format use:" doesn't apply to the line that follows it. Updating the "usage:" to document \definitionx would be nice.

@jwakely: Done. As a drive-by, I also made the line break starred so we won't get a page break there.

I've adopted this for the Networking TS (cplusplus/networking-ts@eec1cc9)

This change has the unfortunate effect of changing references from "3.x" to just "3".

@zygoloid, @jwakely: I'll look into this and will try to find a better solution that restores the references. I'll be in touch.

@jwakely: I changed the way I suppress the TOC entry in 7542c70, which is a superior solution. The first solution did not only break reference labels, but also modified the vertical layout slightly.