Marx and Engels'Theory about tragedy is always under dispute:whether backward classes, negative characters can be treated as tragic roles;

马恩有关悲剧的理论是理论界一直存在争议的问题：落后阶级、反面人物能否作为悲剧人物来写；

One thing to note in terms of backward-compatibility is that the class name closure is now reserved by the PHP engine for storing closures, so any classes that use that name will need to be renamed.

关于向后兼容性值得注意的一点是，PHP引擎现在保留类名closure并用于存储闭包，因此使用该名称的所有类都需要重命名。

Converting existing library classes to work smoothly with generics was no small feat, but as is often the case, backward-compatibility does not come for free.

在转化现有的库类来使用泛型方面没有多少技巧，但与平常的情况相同，向后兼容性不会凭空而来。

So, sum up the last point - after work but also as a backward students "free up classes."

所以，总结出来最后一点是——下了班还要为后进生“无偿补课”。