I'm afraid I couldn't understand the information available about this feature. A canonical link should be the "canonical" or "preferred" version of a web page. An alternate link specifies languages and optional geographic restrictions, according to sources.
With that information, I assume the non-regional version of my website, which displays content in English, should be the only canonical page set. The others should be alternate. For example,
https://127.0.0.1/ca/fr/ should be alternate, while
https://127.0.0.1/ shall be the canonical page.
But there's something that makes me doubt this since I've looked through some popular websites. Now, I'll note that they tend to treat the
https://127.0.0.1/ as the U.S. adaptation of their page. Because of that, I believe the canonical link of each of their pages changes due to the selected region. For example, when visiting the
https://127.0.0.1/, the canonical link is
https://127.0.0.1/, while the alternate ones are
https://127.0.0.1/ca/fr/, etc. When visiting
https://127.0.0.1/bg/, however, the canonical link is suddenly
https://127.0.0.1/bg/. And no matter which the canonical link is, it is among the alternate ones in every case.
https://127.0.0.1/ is both the canonical and an alternate version, which confuses me.
How exactly should these features be used? And shouldn't the canonical link be only canonical and not an alternate one as well? Is it necessary to specify a canonical link if only one version of a particular page exists, such as a page where the visitor selects their region?