Link rel=“canonical”: Should different user guide

问题:

Should 2 different versions of a user guide use a different canonical URL?

Documentation version 1.1.0.Final:

<link rel="canonical" href="http://docs.foo.org/1.1.0.Final/index.html">

Documentation version 1.2.0.Final:

<link rel="canonical" href="http://docs.foo.org/1.2.0.Final/index.html">

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Or should 2 different versions of a user guide use the same canonical URL?

Documentation version 1.1.0.Final:

<link rel="canonical" href="http://docs.foo.org/latestFinal/index.html">

Documentation version 1.2.0.Final:

<link rel="canonical" href="http://docs.foo.org/latestFinal/index.html">

回答1:

Per The Canonical Link Relation from RFC 6596, the canonical link type may only be used for URIs that identify content that is

• duplicative, or
• a superset.

As this is not necessarily the case for different versions of the user guide (because features might be added/removed/changed), the canonical link type must not be used to always point to the latest version. If you want to use canonical, it would have to be self-referential.