16893,Stop or reduce crawling of comment reply ?replytocom URLs,joelhardi,nacin,"(For full background, you can check out the off-topic comments at the ends of #10550 and #16881.)
r16230 (quite appropriately) removed the `rel=""nofollow""` attribute from the Reply to this comment links in the comments display. Since then, users have reported search engines are now crawling these pages (as one would expect). This means unnecessary server overhead (these pages are almost always dynamically generated even when using a caching plugin) and may reduce the frequency search engines crawl ""real"" pages since there are so many of these dummy URLs to index.
Additionally, there may be SEO-related reasons why this is bad. Although that may be largely mitigated by `rel=""canonical""` and the fact that contents of these pages are 99.9% a duplicate of their canonical versions, search engines are also known to penalize sites for having many pages with duplicate content. And, the specification for the canonical attribute states that its use in page-ranking calculations is at the discretion of indexers (i.e., using canonical is no deterministic guarantee of anything).
I'm attaching 2 patches to be considered/discussed separately:
== 1: robots meta tag ==
The first applies the [http://www.robotstxt.org/ robots exclusion standard] to these URLs.
For individual site admins, putting `Disallow: *?replytocom` in your robots.txt is the obvious fix. #11918 would have added this rule to what do_robots() returns, but this was dropped (but that was way before r16230). I would support putting it back in.
My patch general-template.php.17522.diff would add the `` tag (already used when the !WordPress privacy setting is enabled) to the ?replytocom URLs. The pages would still be hit by crawlers but would no longer be indexed -- so, 100% addressing the duplicate indexing issue and rendering moot debates over the effectiveness of ""canonical.""
Compared to robots.txt, this is an imperfect solution to the crawling/server overhead problem because these pages would still have to be at least partially retrieved to read the meta tag. I expect that it will still have a beneficial effect in this area, because well-behaved crawlers will reduce the frequency that they retrieve these noindex URLs.
I've got this code deployed on some live sites to test this idea out (but they previously had a robots.txt rule blocking ?replytocom, so I don't expect instantly useful info).
Even if it's not 100% effective, I think this is an improvement and trivial enhancement that could go into core soon. (this is the dev-feedback item.)
== 2: change links to forms ==
Picking up on an idea filosofo had to replace the links with forms, I've done that with comment-template.php.17522.diff.
Functionally, this is a drop-in replacement, since these are GET forms that produce the same HTTP request as the current tags (please, try them out!).
Although Google has been [http://googlewebmastercentral.blogspot.com/2008/04/crawling-through-html-forms.html crawling forms] for some time, it's only been on an experimental basis and isn't widespread. It also does not affect crawler's page selection or the search engine ranking in any way. So, changing these links to GET forms should sharply reduce (but possibly not eliminate) crawling of URLs. I don't have any data for this so it merits further discussion.
One implementation issue would be that since the tags are now