What are the highlights of changes in the CommonMark flavor?

Would someone please provide some highlights for how the CommonMark flavor is different from the Gruber/Github/StackExchange flavors? I’m sure there’s a mountain of details that were previously unclear and now aren’t, but as an end-user of Markdown, the web page doesn’t make it clear what this changes for me.

What are the big things I have to start writing differently now? Have any of the “why can’t Markdown just do X sensibly?” quirks (e.g., line breaks in lists, or what kind of brackets to use in links, or underscores in words) been worked out? Where am I most likely to encounter divergence (on something I actually care about) between StackExchange or GitHub markdown and Standard Markdown? What (if any) new syntax features have been added?

It’s covered in this topic already:

http://talk.commonmark.org/t/what-changed-in-standard-markdown/15/1

Any specifics you have that aren’t answered by that topic? You can experiment with whatever Markdown you’re curious about with the Dingus at

http://try.commonmark.org