What is BackendFactory in context of react dnd?

Question

I am trying to implement the react-chessboard component. I want a page that contains an empty chessboard and the pieces are kept outside for the user to drag and drop them into the board. By default the board is set to the starting position. In the react-chessboard documentation, I came across a prop called 'customDndBackend' which takes a value of type BackendFactory. I could not find it anywhere so I asked it here. Any help would be appreciated. react-chessboard-npm page

<Chessboard
                className={classes.board}
                boardWidth={
                    window.screen.width < 600 ? 0.9 * window.screen.width : 560
                }
                arePiecesDraggable={true}
                // position={'start'}
                animationDuration={200}
                customBoardStyle={{
                    borderRadius: '4px',
                    boxShadow: '0 5px 15px rgba(0, 0, 0, 0.5)',
                }}
                customDarkSquareStyle={{ backgroundColor: '#A1B57D' }}
                customLightSquareStyle={{ backgroundColor: '#F7F7EE' }}
                customPieces={customPieces()}
                ref={chessboardRef}
            />