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begin
  form2:=TForm2.Create(nil);
  try
    form2.ShowModal;
    if form2.ModalResult=mrOK then
    begin
      ....
    end
  finally
    form2.Free;    
end;					

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  Form2 := TForm2.Create(nil);
  try
    Form2.XYZ := 'Test';
    if Form2.ShowModal = mrOK then
    begin
      ....
    end
  finally
    Form2.Free;    
  end;					

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type
  TForm2 = class(TForm)
  ...
  public
    XYZ: String;
  end;

...

procedure TForm2.Button1Click(Sender: TObject);
begin
  ShowMessage(XYZ);
end;