Google:
We now support a format that allows you to publicly specify your preferred version of a URL. If your site has identical or vastly similar content that's accessible through multiple URLs, this format provides you with more control over the URL returned in search results. It also helps to make sure that properties such as link popularity are consolidated to your preferred version.
Monen ei-niin-URL-tietoisen julkaisujärjestelmän elämä helpottui juuri huomattavasti.