I suspect I heard about the Emacs zencoding mode from its (I believe) original author, Chris Done—he did a screencast about using Emacs for Haskell development that I found interesting, and I imagine that I found a reference while looking at his material about that.
Now, however, is the time—I’m doing some HTML writing these days, so I thought I’d go back and start learning it.
So, the magic keystroke is
C-j (zencoding-expand-line) or
C-RETURN. The language…well, I will probably have to refer back to the cheat-sheet on the github page now and again—it’s like CSS, without entirely being CSS—but I expect it will take a lot of the really repetitive boilerplate out of writing HTML for me.