calcFetchSize( itemSel, maxRows = Number.POSITIVE_INFINITY ) {
		const columns = getNeededColumns( itemSel );
		const rows = min( getNeededRows( itemSel ), maxRows );
		const remaining = this.offset % columns;

		return ( columns * rows ) + ( remaining > 0 ? columns - remaining : 0 );
	}
Calculate how many items are needed to completely fill the container
@param {string} itemSel
@param {number?} maxRows