It seems to be only a very rudimentary implementation of a yaml major mode. The only thing that it does better is that it works faster and seems to do more consistent highlighting. And I actually like what you describe as “graphical flashing” because it gives you immediate feedback when something is wrong. Yet I admit it is annoying too. Also, yaml-mode indentation while better still needs getting used to in comparison to other modes. I am back at using yaml and yaml-pro.