Registration of S3 class "zoo" as a formally defined class. Used here to allow the "zoo" class to appear in method signatures.
S3类"zoo"作为一个正式定义的类注册。在这里,让“"zoo"类出现在方法签名中。
类对象----------Objects from the Class----------
A virtual Class: No objects may be created from it.
可能会从它创建一个虚拟类:没有对象。
插槽----------Slots----------
.S3Class: Object of class "character"
.S3Class:对象类"character"的