What Information Have the Engines Provided About the Canonical URL Tag?

Google:

Is rel="canonical" a hint or a directive?
It's a hint that we honor strongly. We'll take your preference into account, in conjunction with other signals, when calculating the most relevant page to display in search results.


Can I use a relative path to specify the canonical, such as ?
Yes, relative paths are recognized as expected with the tag. Also, if you include a link in your document, relative paths will resolve according to the base URL.

Is it okay if the canonical is not an exact duplicate of the content?
We allow slight differences, e.g., in the sort order of a table of products. We also recognize that we may crawl the canonical and the duplicate pages at different points in time, so we may occasionally see different versions of your content. All of that is okay with us.


What if the rel="canonical" returns a 404?
We'll continue to index your content and use a heuristic to find a canonical, but we recommend that you specify existent URLs as canonicals.

What if the rel="canonical" hasn't yet been indexed?
Like all public content on the web, we strive to discover and crawl a designated canonical URL quickly. As soon as we index it, we'll immediately reconsider the rel="canonical" hint.

Can rel="canonical" be a redirect?
Yes, you can specify a URL that redirects as a canonical URL. Google will then process the redirect as usual and try to index it.


What if I have contradictory rel="canonical" designations?
Our algorithm is lenient: We can follow canonical chains, but we strongly recommend that you update links to point to a single canonical page to ensure optimal canonicalization results.



Yahoo!:

The URL paths in the tag can be absolute or relative, though we recommend using absolute paths to avoid any chance of errors.

A tag can only point to a canonical URL form within the same domain and not across domains. For example, a tag on http://test.example.com can point to a URL on http://www.example.com but not on http://yahoo.com or any other domain.

The tag will be treated similarly to a 301 redirect, in terms of transferring link references and other effects to the canonical form of the page.

We will use the tag information as provided, but we’ll also use algorithmic mechanisms to avoid situations where we think the tag was not used as intended. For example, if the canonical form is non-existent, returns an error or a 404, or if the content on the source and target was substantially distinct and unique, the canonical link may be considered erroneous and deferred.

The tag is transitive. That is, if URL A marks B as canonical, and B marks C as canonical, we’ll treat C as canonical for both A and B, though we will break infinite chains and other issues.


Live/MSN:

This tag will be interpreted as a hint by Live Search, not as a command. We'll evaluate this in the context of all the other information we know about the website and try and make the best determination of the canonical URL. This will help us handle any potential implementation errors or abuse of this tag.

You can use relative or absolute URLs in the “href” attribute of the link tag.

The page and the URL in the “href” attribute must be on the same domain. For example, if the page is found on “http://mysite.com/default.aspx”, and the ”href” attribute in the link tag points to “http://mysite2.com”, the tag will be invalid and ignored.
o However, the “href” attribute can point to a different subdomain. For example, if the page is found on “http://mysite.com/default.aspx” and the “href” attribute in the link tag points to “http://www.mysite.com”, the tag will be considered valid.

Live Search expects to implement support for this feature sometime in the near future.

Yes... you heard it right... If everything goes well, you can watch videos in 3D from YouTube.

Google is still working on this, hopefully will be ready to launch soon. This 3D videos cannot be embedded.


YouTube has now invited users to upload our own 3D video.

How to do this...?
Here is the tips, taken from YouTube blog

Tag the video with yt3d:enable=true, and leave the link in a comment on this blog.

Some basics around shooting 3D videos (this isn't easy, so patience is key):

* Use two cameras arranged like a pair of eyes.
* Start both cameras recording simultaneously.
* In your video editing program, place the footage for the left and right eyes together in the frame side by side, with the right eye on the left and the left eye on the right.
* Upload your video! Edit your videos tags and add yt3d:enable=true. If video is widescreen, add yt3d:aspect=16:9 too.

As we know, micro blogging or Twitter is one of the fastest growing social media. But are we making enough use of this?
Twitter couldn’t find out yet how they can make money out of it. But others are making use of it. E.g. Dell.
There was some news that the revenue of Dell has been increased tremendously after them trying to market products through Twitter.
How can we make use of Twitter in PPC, or Search Engine Marketing? The main advantage of Twitter from a Search Engine Marketing point of view is that we can easily identify what is happening in the market. What people are talking about our brand? What people are talking about our competitors?
We can find out who is talking about our brands on Twitter, know the influence level of our brand and competitors brand on them
Then just analyze the influence and reputation level of twittees. This will help us to make a campaign strategy.

Now how to search in Twitter? Its easy.
Just go to Twitter Search and type the keyword you would like to know about. Thats it...