Several weeks after Google rolled out support for Preferred Sources globally, Google added official help documentation for site owners to use to help them understand what it is all about and how to encourage their readers to subscribe to your site as a preferred source.
In December, Google rolled out Preferred sources globally after rolling it out in the US and India in August and beta testing it in June.
Now the new help documentation is available here if you need it.
Google wrote:
If you're a website owner, you can help your audience find your publication as a preferred source in Google Search. When a user selects your site as a preferred source, your content is more likely to appear for them during relevant news queries in "Top Stories".
As a reminder, if you love this site, you can add this site as a preferred source on Google by clicking here.
The preferred sources feature is available globally in English for queries that trigger the "Top Stories" feature.
Only domain-level and subdomain-level sites are eligible to appear in the source preferences tool. For example, https://www.example.com/ and https://code.example.com/ are eligible for preferred sources, but the subdirectory https://www.example.com/blog isn't eligible.
Google added, "These methods are examples on how you can build your audience and help people find your site as a preferred source. It's not required to do them in order to appear as a preferred source."
Here is a screenshot of the help document, so I can archive it myself:
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