Each functions in a slightly different way.

每种功能的方式略有不同。

Because the cruise control team didn't write that, they're going to need good documentation about what each function in the code does, and a well-defined Application Programming Interface -- or API for short.

因为巡航控制团队没有编写这些代码，所以他们需要关于代码中每个函数的作用的良好文档，以及定义良好的应用程序编程接口——或简称 API。