It is the mark of an educated man to look for precision in each class of things just so far as the nature of the subject admits . 一个有教养人的标志在于，他能在问题性质的许可范围内追寻每一类事物的精确含义。
2.
Identifies class of thing on which permission exists 标识存在权限的对象的类。
3.
Identifies class of thing on which property exists 标识属性所在项的类。
4.
Description of the class of thing on which property exists 对于属性所在项的类的说明。
5.
Is used to declare that an information item in the xml schema represents some class of thing 用于声明xml模式中的信息项代表某类事物。
