Atom Threading Extensions (`thr:`, [RFC 4685](http://tools.ietf.org/html/rfc4685)) could be used by internal representation (`libearth.feed`). Also, [RSS Slash Module](https://developer.mozilla.org/en-US/docs/Web/RSS/Article/Why_RSS_Slash_is_Popular_-_Counting_Your_Comments) can be translated to `thr:`.
Atom Threading Extensions (
thr:, RFC 4685) could be used by internal representation (libearth.feed). Also, RSS Slash Module can be translated tothr:.