GitHub 自家版本的 Markdown 給出了正式的規格，GitHub Flavored Markdown Spec：「A formal spec for GitHub Flavored Markdown」。
規格裡面把標出 GFM 版本所特有的特性：
When reviewing the GFM spec, you can clearly tell which parts are GFM-specific additions because they’re highlighted as such. You can also tell that no parts of the original spec have been modified and therefore should remain fully compliant with all other implementations.
有種內部在實做時順便整理出來的感覺...