The primary constructor, which is the body of the entire class, has a parameter list that takes a label string and a list of callback functions.
主构造函数，类的主题，有一个参数列表来接受标签字符串和回调函数的列表。
If the return type and parameter list of two functions declarations match exactly, then the second declaration is treated as a redeclaration of the first.
如果两个函数声明的返回类型和形参表完全匹配，则将第二个函数声明视为第一个的重复声明。
The Parameters list also displays parameter information for nested functions.
“参数”列表还显示嵌套函数的参数信息。
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