SEO Nicnacs - Canonicalization

Having the same content on several pages create what SEO:s call duplicate content. To put it briefly duplicate content may confuse search engine robots of the contents true origin and whom to credit for it. The problem is especially prevalent in CMS:s such as Wordpress, Joomla, Drupal, but also for ecommerce platforms like Magento. A few years ago a new metatag commonly referred to as rel=canonical was introduced to remedy the problem, and this is what it would look like in the source code:

Here is a short example portraying the problem:

You have a website page with the following URLs:

a) http://www.seoblogg.se

The content of this page is also available on the following page:

b) http://seoblogg.se