What is rel="bookmark"?

While looking for linking conventions regarding permalink locations, I found a reference on Wikipedia to <a rel="bookmark" href="..."> being used for permalinks. I’m not sure I’ve ever noticed or used that. I didn’t find any mentions of people actually using it that way.

Mostly I found secondhand references to other references to the HTML spec (yes, it’s official!), which has this clear as mud description:

The bookmark keyword may be used with a and area elements. This keyword creates a hyperlink.

The bookmark keyword gives a permalink for the nearest ancestor article element of the linking element in question, or of the section the linking element is most closely associated with, if there are no ancestor article elements.

So, should I use this on the permalink, well, link on my post, or not? Should I use it only on multi-post pages like tag/category archives? Or in a table of contents?

The best reference I found, rel="bookmark" also does not mean what you think it means is more clear: It should go anywhere you would link to a permalink from the same material. So:

• Single blog post on a page, linking to itself? Yes!
• Time or category archive pages, with complete posts or significant chunks of them, linking to each individual post’s page? Yes!
• Table of contents listing just titles and summaries? NO!
• Long page with multiple posts, where the permanent versions of those posts are on that same page, each with a permalink pointing to that section on that page? Yes!

The same article also points out that it’s effectively obsolete, since just about everyone uses permalinks now, but hardly anyone puts rel="bookmark".

I decided to add it when I updated my templates, because why not?