Last modified: 2014-11-17 09:21:14 UTC
Should be relatively self-explanatory, here's the link to the rel value's info: http://microformats.org/wiki/rel-discussion
Change 134872 had a related patch set uploaded by Matěj Grabovský: (bug 63198) Add rel=discussion to talkpage tabs https://gerrit.wikimedia.org/r/134872