UPDATE id:syohex told me that the forked version of markdown-mode is hosted on github and fixed some bugs including weird behaviour of dabbrev-expand. I checked it and confirmed it works correctly. I strongly recommend to use it instead of my poor implementation. https://github.com/milkypostman/markdown-mode Markdown is popular markup language today. Many web sites support markdown such as GitHub
![markdown-highlight-mode.el - @kyanny's blog](https://cdn-ak-scissors.b.st-hatena.com/image/square/862d540809c2ca9ce640e514738db2d91571e0bb/height=288;version=1;width=512/http%3A%2F%2Fcdn-ak.f.st-hatena.com%2Fimages%2Ffotolife%2Fa%2Fa666666%2F20130114%2F20130114180136.png)