My understanding of the CMS Versions, Major and Minor is the XARA HTML generator, c.f., <meta name="Generator" content="Xara HTML filter v.9.6.1.39"/> for v17.0
v10 has generator version 7.0 and Xara Xtreme 5.1 is version 2.2 (<meta name="Generator" content="Xara HTML filter v.2.2.0.675"/>).

CMS has nothing to do with actual content management systems but
A CMS will sometimes include a meta tag within the html of each page. This is usually a "generator" tag like <meta name="generator" content="What CMS" /> but could also be "application-name", "Powered-By" or anyting else the CMS creators decide to use.
This is the more telling as it shows how much Xara loses against each version it delivers.
Map generator version to product version and you can see the trend.

Acorn