Reference TIndexedList<TItem>

  TIndexedList<TItem> = class(TList<TItem>)
  protected
    { AddItem checks for duplicates }
    procedure AddItem(constref Item: ItemType); override;
    { Allow, ignore, or error on adding a matching item }
    property Duplicates: TListDuplicates read FDuplicates write FDuplicates;
  public
    { Returns true if the list contains item }
    function Contains(const Item: ItemType): Boolean;
    { Returns the index of the item or -1 if it cannot be found }
    function IndexOf(const Item: ItemType): Integer; virtual; abstract;
    { Remove the item by value returning true if it was found }
    function Remove(const Item: ItemType): Boolean;
  end;