What should your API documentation describe? code example

Example: what is api documentation

The API documentation is a complete, 
accurate technical writing giving
instructions on how to effectively 
use and integrate with an API. It is
a compact reference manual that has 
all the information needed to work with
the API, and helps you answer all the
API testing questions with details on 
functions, classes, return types, arguments, 
and also examples and tutorials.