API Documentation
The API Documentation is automatically build from PHPDoc comments into the Gishiki source code.
The API Documentation is the most advanced and up-to-date documentation you can find, but you will need to know how to use Gishiki before understanding that documentation.
The API Documentation is perfect to have an overview of what you can do using Gishiki and how Gishiki is organized internally.
Accessing the docs
You can access the API Documentation from here.
If you are totally unable to understand what is described there just don't worry about it, you can do amazing things even without reading that thing!