procedure TfrmMain.pnlLeftUnDock(Sender: TObject; Client: TControl;
NewTarget: TWinControl; var Allow: Boolean);
begin
  if (Sender as TPanel).VisibleDockClientCount = 1 then
  begin
    (Sender as TPanel).Width := 1;
  end;
end;
  
procedure TfrmMain.pnlLeftDockDrop(Sender: TObject;
  Source: TDragDockObject; X, Y: Integer);
begin
  (Sender as TPanel).Width := max(source.Control.UndockWidth,(Sender as TPanel).Width);
end;
  
procedure TfrmMain.pnlLeftDockOver(Sender: TObject;
  Source: TDragDockObject; X, Y: Integer; State: TDragState;
  var Accept: Boolean);
begin
  if State = dsDragEnter then
  begin
    (Sender as TPanel).Width := max(Source.Control.UndockWidth, (Sender as TPanel).Width);
  end
  else
  begin
    if State = dsDragLeave then
    begin
      (Sender as TPanel).Width := 1;
    end;
  end;
end;


//delphi/6875