Show my own help dialog when user clicks the biHelp border icon

Show my own help dialog when user clicks the biHelp border icon

type
  TForm1 = class(TForm)
  private
    procedure wmNCLButtonDown(var Msg: TWMNCLButtonDown); message WM_NCLBUTTONDOWN;
    procedure wmNCLButtonUp(var Msg: TWMNCLButtonUp); message WM_NCLBUTTONUP;
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.wmNCLButtonDown(var Msg: TWMNCLButtonDown);
begin
  if Msg.HitTest = HTHELP then
  begin
    Msg.Result := 0; // swallow mouse down on biHelp border icon
  end
  else
    inherited;
end;

procedure TForm1.wmNCLButtonUp(var Msg: TWMNCLButtonUp);
begin
  if Msg.HitTest = HTHELP then
  begin
    Msg.Result := 0;
    ShowMessage('Hi!'); // Show your help here
  end
  else
    inherited;
end;