A CLR type definition consists of zero or more members. The members of a type control how the type can be used as well as how the type works. Each member of a type has its own access modifier (e.g., public, internal) that controls access to the member. The accessible members of a type are often referred to collectively as the contract of the type.
(一个类的可访问成员被整体的称为类的契约)
是一种约定。代表这个类可以做什么。