What are Canonical tags?
Canonical tags help search engines understand whether or not a URL is the master page or a copy of it. This helps to stop search engines like Google from indexing duplicate pages. Your home page, for example, can be found via many different URLS that all represent the page (https://yoursite and www.yoursite for example). Canonical tags remove the confusion and help Google rank the right pages. All pages should include a canonical tag to avoid possible duplication.
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