梦幻西游天眼珠合成:delphi的自定义过程何时被调用?

delphi的自定义过程何时被调用?如下例中的"procedure WMHotKey(var Msg : TWMHotKey); message WM_HOTKEY;"这个过程

源程序：

unit Unit1;
interface
uses
Windows, Messages, Forms, Dialogs, Classes, Controls, StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure FormClose(Sender: TObject; var Action: TCloseAction);
private
{热键标识ID}
id: Integer;
procedure WMHotKey(var Msg : TWMHotKey); message WM_HOTKEY;
{ Privat-Declarations}
public
{ Public-Declarations}
end;
var
Form1 : TForm1;
implementation
{$R *.DFM}

{捕获热键消息}
procedure TForm1.WMHotKey (var Msg : TWMHotKey);
begin
if msg.HotKey = id then
ShowMessage(’Ctrl+Alt+R键被按下!’);
form1.Visible :=true;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
{首先判断程序是否已经运行}
if GlobalFindAtom(’MyHotkey’) = 0 then
begin
{注册全局热键Ctrl + Alt + R}
id:=GlobalAddAtom(’MyHotkey’);
RegisterHotKey(handle,id,MOD_CONTROL+MOD_Alt,82);
end
else
halt;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
close;
end;

{退出时释放全局热键}
procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
UnRegisterHotKey(handle,id);
GlobalDeleteAtom(id);
end;
end.
谢谢ramu的答复！！
我是想知道delphi中的过程调用机制，如我的例子中“procedure WMHotKey(var Msg : TWMHotKey)； message WM_HOTKEY；”这个过程，它是如何被调用的。又如果我编了一个非事件处理过程，而且也未在任何过程的代码中引用它，请问这个过程是否永远不会被调用？？？？
知道的请说详细点