Do we need to be that strict about a second version number parameter, if it's optional to begin with?

Arbitrary description text is hardly parse-able.  _Machine-readable_ values natively deliver useful answers to interesting questions:

* What is deprecated in version x.y.z?
* What has been deprecated _since_ version x.y.z?
* What is scheduled for removal in version x.y.z?

The more data is machine-readable, the more data can be derived.  Just the above answers would significantly help maintainers as well as users of larger FOSS projects.

Suggested synopsis:
```
 @deprecated [<"Semantic Version"> [<"Semantic Version">]] [<description>]
```