*Charles McCathieNevile*:
>
> <ruby class="acron">
> <rb>NATO</rb><rt>North Atlantic Treaty Organisation</rt></ruby>'s

That's not really better than

  <acronym title="North Atlantic Treaty Organisation">NATO</acronym>'s.

A UA should know to do the right thing when encountering

  <acronym>NATO</abbr>'s

or

  <abbr>NATO</abbr>'s.

Because a UA can never know all initialisms, acronyms and other abbreviations
of every language, a author should be able to help it out---outside the
mark-up. It's quite similar to automatic hyphenation.