If you want to include Flattr in your RSS or Atom feeds then this is the recommended way for doing so. Including Flattr in a feed can be useful for podcasts and similar but the same method can also be used in other scenarios.
You include Flattr in your feeds by adding payment links, using the standard payment relation, to your feed entries that you point directly to (without any redirects) auto-submit URL:s for those feed entries.
In an Atom feed add something like this to an entry:
<link rel="payment" href="https://flattr.com/submit/auto?url=https%3A%2F%2Fdevelopers.flattr.net%2F&user_id=flattr" type="text/html" />
In an item in a RSS feed add this instead:
<atom:link rel="payment" href="https://flattr.com/submit/auto?url=https%3A%2F%2Fdevelopers.flattr.net%2F&user_id=flattr" type="text/html" />
And in a RSS feed also make sure that the RSS-container itself knows of the atom:link-tag by adding the atom-namespace:
<rss xmlns:atom="http://www.w3.org/2005/Atom">
What is this standard payment relation that we suggest you to use? It's the one defined in the "Web Linking" standard RFC5988 and fits the use case perfectly, being defined as usable for eg. tipjars.
The "Web Linking" standard defines a common link relations registry for Atom-feeds, HTML-documents, HTTP Link-headers etc. - thus this method isn't strictly limited to feeds, but feeds are the primary use case that we see.
With auto-submit URL:s as payment-links all clients already supporting payment-relations will automatically support Flattr links, but clients that wants to do Flattr specific integrations can also do so.
Eg. mobile clients that wants a better UX-flow for Flattr can implement such by checking payment-links for URL:s matching the pattern of auto-submit URL:s (links starting with "https://flattr.com/submit/auto") and use those URL:s for the API resources /things/lookup and /flattr to get more info about them or to flattr them.
We discourage hiding auto-submit URL:s behind redirects – clients should be able to expect that a Flattr payment link is identifiable by just matching it against a pattern.