Обработка событий: где генерируются параметры

comboBoxEdit1.SelectedIndexChanged += new System.EventHandler(
    this.comboBoxEdit1_SelectedIndexChanged);
//...
 private void comboBoxEdit1_SelectedIndexChanged(object sender, System.EventArgs e)
{ //действия }

+= new System.EventHandler(this.comboBoxEdit1_SelectedIndexChanged);

public event EventHandler MyEvent;
 
private OnMyEvent() {
   if (MyEvent != null) {
      MyEvent(this, new EventArgs()); //вызываем все обработчики нашего события
   }
}

private static readonly object EVENT_SELECTEDINDEXCHANGED = new object();
 
public event EventHandler SelectedIndexChanged
{
    add
    {
        base.Events.AddHandler(ComboBox.EVENT_SELECTEDINDEXCHANGED, value);
    }
    remove
    {
        base.Events.RemoveHandler(ComboBox.EVENT_SELECTEDINDEXCHANGED, value);
    }
}

private sealed class ListEntry
{
    internal EventHandlerList.ListEntry next;
    internal object key;
    internal Delegate handler;
    public ListEntry(object key, Delegate handler, EventHandlerList.ListEntry next)
    {
        this.next = next;
        this.key = key;
        this.handler = handler;
    }
}
private EventHandlerList.ListEntry head;
 
public void AddHandler(object key, Delegate value)
{
    EventHandlerList.ListEntry listEntry = this.Find(key);
    if (listEntry != null)
    {
        listEntry.handler = Delegate.Combine(listEntry.handler, value);
        return;
    }
    this.head = new EventHandlerList.ListEntry(key, value, this.head);
}

private void comboBoxEdit1_SelectedIndexChanged(object sender, System.EventArgs e)

Их же инициализирует SelectedIndexChanged()?
 //То есть передает параметры для (object sender, System.EventArgs e).