Version 0.18 of the spec has been released (release notes).
The reference implementations have been updated to conform.
Several other changes of note:
The spec, javascript implementation, and C implementation now all live in separate repositories.
The license for the reference implementations has been changed to the 2-clause BSD license.
The dingus now uses the ACE editor and provides scroll sync and highlighting of the part of the rendered document corresponding to cursor position in the source.
Both implementations now offer an option for “smart punctuation” (straight quotes to curly quotes, -- and --- to en and em- dashes, ... to ellipses).
Will specification for “smart punctuation” be published?
It really should be, and the test suite (test/smart_punct.txt in cmark) could be amplified to a spec. But this is not part of official CommonMark syntax at this point, so not part of the main spec.
Specifically interesting questions.
When " is converted to open curly quote and when to closed?
Quotes work much like emphasis markers. We try to pair right-flanking ones with left-flanking ones. Unmatched single quotes are treated as right quotes. This gives good results for, e.g.
'Tis the season to be 'jolly'.
(Most smartypants filters I have seen will incorrectly make the single quote before Tis into a left single quote.)
Is — always converted to em-dash?
Yes. However, note that punctuation that is backslash-escaped will not be made “smart.”
(Most smartypants filters I have seen will incorrectly make the
single quote before Tis into a left single quote.)
That’s because contractions are a more common use case than unpaired
left quotation marks.
Sorry, I’m not sure I follow. Yes, contractions are more common, but in contractions you should have a right single quote, whether it occurs inside a word (it’s) or at the beginning (’tis). Left single quote should only be used when you have a matched pair. cmark gets this right, and most others get it wrong, because they don’t try to match quotes.
