Illustration: You may have an e-commerce website with item web pages for different sizes of a particular t-shirt.   You specify the key URL as the search engine could have problem determining which a single should be the main URL.  The following tutorial will provide you with tips on how https://www.presta-addons-modules.com/en/seo/prestashop-seo-automatic-hreflang-tags-canonical-tags-on-all-pages.html