NOTE:Support has now been officially announced. See the Google, Yahoo, MSN Unite On Support For Nofollow Attribute For Links post for more.
Dave Winer posted a cryptic Watch This Space post yesterday, pointing at a page that many have interpreted to mean that Google will be providing support for a "nofollow" attribute that can be added to links.
For example, the HTML code for an ordinary link might look like this:
<a href="http://www.site.com/page.html">Visit My Page</a>
HTML specs (3.2, 4.0, XHTML 2.0) allow for links to have additional information associated with them. The rel attribute is designed to allow authors to express particular relationships about the current document to the page it is linking to.
In Winer's post, he makes use of a nofollow rel attribute in links that appear in the comments of his post, such as like this:
<a href="http://www.site.com/page.html" rel="nofollow">Visit My Page</a>
The speculation of those who spotted this (see Robert Sayre with a supportive comment from Dave, Simon Willison, others) is that Google will be providing support of the nofollow attribute in some way to help combat comment spam on blogs (and by extension, anywhere people may find publicly-contributed links to cause problems).
Why Google? In the past, Dave has suggested that comment spam is a Google problem -- and earlier this week, he also posted a note saying he'd heard from a the "only" that could solve a "big" problem on the internet.
What might the nofollow attribute do? The closest thing we have to it at the moment is the nofollow attribute for the meta robots tag. That attribute is a way to tell search engines not to follow links from a page they may have found.
It's important to note that the attribute was intended for site owners who wanted to prevent search engines from indexing other pages they link to from within their own sites, not as a mechanism for preventing the indexing of pages of sites outside their control. No does it allow this. If there was another way to find a page (on the site owner's site or not) -- and if the page itself is not blocked somehow from being indexed -- then it would still get listed.
So a nofollow attribute associated with a link itself isn't likely to prevent the page the link points at from being indexed. After all, search engines will likely find those pages in other ways, and those pages probably won't have spider blocks placed on them.
Instead, a nofollow attribute is likely to be treated as an "ignore" or "don't count" flag. It's the way for a web author to say, "I don't care about these links -- nor should you."
How might Google react to it? That remains to be seen. It might decide not to index the link at all -- so it wouldn't record the text of the link, nor the fact that the link points at another page -- depriving that page of a possible PageRank rise. Or, it could decide to index the information but not weight it as heavily.
Whatever the case, it won't stop blog comment spam -- nor other types of link spamming across the web. But it's a start, and more important, it gives authors more control over their pages. I'm all for that.
My main disappointment, should the mechanism emerge, is that it would have come unilaterally from Google. Despite what Dave thinks, comment spam is not a Google problem. It's a search problem in general, and it would be nice to see the search engines work together to solve the wide range of issues that web authors (not just bloggers) have.
More on this in my past Comment Spam? How About An Ignore Tag? How About An Indexing Summit! post, where I talk about the idea of an "ignore" tag or more important, an indexing summit to discuss publisher needs and controls. We're doing that at our SES New York show, by the way. I hope to get some search engine reps to come hear and discuss what publishers of all types are looking for.
Also see Nick's Rumour - Google About To Kill Comment Spam post and comments at Threadwatch. I've chimed in along with others about what might happen, how it might fit in with things and what may or may not work. Also some nice thoughts also from Peter Van Dijck and a summary from Steve Rubel.
Postscript: We've also got a thread going on the topic now in our forums, where you can comment or discuss: Discussion on 'Google To Add "Nofollow" Tagging' blog