Text Content Canonical
Text content marked as canonical via the rel=”canonical” tag and link in the page header will be regarded as the original and will gain rank against other pages within the same site that have duplicate content.
The original and content duplicate’s canonical tag should carry the link to the canonical page. In the case of the canonical page, the link is just pointing to itself.
So in the page header for this page, the tag looks like this:
<link rel=”canonical” href=”https://rankpower.com/articles/text-content-canonical/” />
Notice the path in that link ( > articles > text content canonical ) – it may not be the actual path that you have in the browser to view this post and this post might be reached through several different breadcrumb links too.
The canonical tag works across domains too, so when you are using someone else’s content and your page is a essentially a duplicate from that of another website, use the canonical tag to point to the original.
Two duplicate pages both marking themselves as canonical will still be competing with each other. Google will not be able to determine the original and the version gaining rank may be selected based on other factors.
Here’s some help form other trusted sources in regards to the canonical tag:
rel=canonical, The Ultimate Guide – by Yoast SEO.
SEO Best Practices for Canonical URLs + the Rel=Canonical Tag – Rand Fishkin at Moz