(if it's undesirable for a link type definition to differ from 'a'/'area' to 'link', dump this issue)

The spec about the 'rel' keyword 'tag' states:
"The tag keyword indicates that the tag that the referenced document represents applies to the current document."

I think it would be useful if the tag (when linked with the 'a'/'area' element) applies to its nearest article or body element ancestor, instead (which is the case for the 'address' element, too).

Thereby a page listing several articles could make use of the 'tag' keyword:

<section>
  <h1>Recent articles</h1>

  <article>
    <h1>My first cooking lesson</h1>
    <p>… — <a href="/blog/cooking-lesson">Read more</a></p>
    <footer>Tagged with <a href="/tags/cooking" rel="tag">Cooking</a></footer>
  <article>

  <article>
    <h1>I scored two goals</h1>
    <p>… — <a href="/blog/two-goals">Read more</a></p>
    <footer>Tagged with <a href="/tags/football" rel="tag">Football</a></footer>
  <article>

</section>

With the current definition, the tags "Cooking" and "Football" apply to the whole page. 
With my proposed addition, the tag "Cooking" applies only to the first article snippet, the tag "Football" only to the second.