[8.2.1 定义语法](8.2.1%E5%AE%9A%E4%B9%89%E8%AF%AD%E6%B3%95.md) [8.2.2 内部实现](8.2.2%E5%86%85%E9%83%A8%E5%AE%9E%E7%8E%B0.md)