The spec has been updated to 0.28:
A list of changes is available here:
Thanks to all who contributed, and especially to Yuki Izumi, Aidan Woods, Matthias Geier for their contributions to the spec; Phil Turnbull, Yuki Izumi, Nick Wellnhofer, Kevin Wojniak, Martin Mitáš, Azamat H. Hackimov for their contributions to cmark; and Erik Edrosa, muji, and Colin O’Dell for their contributions to commonmark.js.
Note that, thanks to Phil Turnbull, cmark has been included in Google’s oss-fuzz project for continuous fuzzing. Several bugs have been identified by the fuzzer and fixed.