我们需要了解的第一个动态数据类型是 置换。
The first type of dynamic data to look at is the substitution.
它们也倾向于使用动态数据类型，即程序员无需定义他们变量所属的数据类型。
They also tend to be dynamically typed, meaning programmers don't need to specify what type of data their variables will hold.
通过观察我们UI中的动态数据类型，我们可以得到应用中需要的不同模型的主意。
By looking at the types of dynamic data in our UI, we can get an idea of the different models needed for our application.
应用推荐