请教关于作用域和委托的问题（附MSDN示例）

MSDN中使用回调方法检索数据的案例
https://msdn.microsoft.com/zh-cn/library/ts553s52(v=vs.110).aspx

using System;
using System.Threading;

public class ThreadWithState
{
    private string boilerplate;
    private int value; 
    private ExampleCallback callback;     

    public ThreadWithState(string text, int number, ExampleCallback callback)
    {
        boilerplate = text;
        value = number;
        this.callback = callback; 
    }    

    public void ThreadProc()
    {
        Console.WriteLine(boilerplate, value);
        if (callback != null) 
            callback(1);
    }
}

public delegate void ExampleCallback(int lineCount);

public class Example
{
    public static void Main()
    {        
        ThreadWithState tws = new ThreadWithState(  "This report displays the number {0}.",42, new ExampleCallback(ResultCallback) ); 

        Thread t = new Thread(new ThreadStart(tws.ThreadProc));
        t.Start();
        Console.WriteLine("Main thread does some work, then waits.");
        t.Join();
        Console.WriteLine( "Independent task has completed; main thread ends.");  
    }    

    public static void ResultCallback(int lineCount)
    {
        Console.WriteLine(   "Independent task printed {0} lines.", lineCount); 
    }
}

问题1：public delegate void ExampleCallback(int lineCount);这个语句，不在主程序中，也没有包含在其他的类中，为什么可以这样写？不是说“所有可执行的 C# 代码都必须包含在类中”吗？为什么ExampleCallback在public class ThreadWithState{}类中是可见的？
问题2：如果 t.Start()很快就执行完了，那么 t.Join()是否还会起作用？

问题1补充：为什么ExampleCallback在public class ThreadWithState{}类中是可见的？

问题1补充：为什么ExampleCallback在public class ThreadWithState{}类中是可见的？