That is, if a function has a certain set or range of valid values for its arguments, an assertion to this effect can be placed as the first line of code in the function.

那就是说，如果函数有确定的有效值集合或范围可作为参数，可以将检验参数是否有效的断言放在该函数代码的第一行。

youdao

These layers and be added or removed dynamically and you can change each layer as it has a track that lets you change it as a function of time by inserting keys at certain frames in the track.

这些层可以被动态的增加或删除，你也可以对这些层进行改动，因为每层都有一个轨道，你可以在轨道中的特定时间点加入关键帧到达改变动画的目的。

youdao

This namespace declaration is required for any application that USES the library since the user-defined function has to be in a certain namespace.

任何使用该库的应用程序都需要这个名称空间声明，因为用户定义的函数必须存在某个名称空间中。

youdao

Arguably, archived email, handled the right way, could perform the same function, essentially, a certification that a document was created at a certain time and has not been altered.

FORBES: After The Post Office