Since 7.2 Blizzard has started implementing an official, text based, API documentation.
APIInterface offers an interface to navigate this documentation more easily, and without spamming text in your chatwindow.
For functions, a textbox also provides an easy way to copy paste said function with variable declaration and names.
As this addon uses the official documentation, any future documentation will automatically be supported.
The interface can be accessed by typing either /apii or /apiinterface