Google, Yahoo and Microsoft unite with one common goal and that is to clean up what is called the Canonical Link Tag. The three big search engines agreed to the manage canonicalization issue with the use of a common tag.

We are announcing our support for a new HTML tag, the
tag, which helps reduce duplicates by documenting the preferred URL form to access each page. When you use the
tag, you can indicate the canonical URL form for crawlers to use for each page of content, no matter how it was retrieved. This puts the preferred URL form with the content so that it is always available to the crawler, no matter which session id, link parameter, sort parameter, parameter order, or other source of variance is present in the URL form used to access the page, Yahoo! Search's Director Product Management Priyank Gar wrote on a press released.

This means that it would enable the search engines to avoid indexing multiple links for the same webpage because the web is full of duplicate content. Search engines will index and display the canonical version; searchers will only see one version in results

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