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A canonical link element is an HTML element that helps webmasters prevent duplicate content issues by specifying the "canonical" or "preferred" version of a web page as part of search engine optimization. It is described in RFC 6596, which went live in April 2012. == Purpose == A major problem for search engines is to determine the original source for documents that are available on multiple URLs. Content duplication can happen in a lot of ways. The most common reasons for duplication are * Duplication due to GET-parameters * Duplication with multiple URLs due to CMS * Duplication due to accessability on different hosts/protocols * Duplication due to print versions of websites Duplicate content issues occur when the same content is accessible from multiple URLs. For example, Canonical tags can also be useful to solve www and non-www duplicate content—where two URLs, identical except that one begins with "www" and other does not, point to the same page. This particular problem can be solved by proper use of the canonical tag.In February 2009, Google, Yahoo and Microsoft announced support for the canonical link element, which can be inserted into the section of a web page, to allow webmasters to prevent these issues. The canonical link element helps webmasters make clear to the search engines which page should be credited as the original.抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Canonical link element」の詳細全文を読む スポンサード リンク
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