It's not accurate to say AsciiDoc only has a single implementation, there is the original AsciiDoc written in Python, and also there is AsciiDoctor written in Ruby. Unfortunately, AsciiDoctor is merely _mostly_ compatible and deliberately opted to not support some features. (And being Ruby, GitHub will use AsciiDoctor to render AsciiDoc files; whether you should conform your documents to this environment depends on w…
but without support for includes. ;_;