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I'm implementing an application for macOS in which I use an NSCollectionView as a sort of timeline. For this I use a custom subclass of NSCollectionViewFlowLayout for the following reasons:1. I want the items to be scrollable horizontally only without wrapping to the next line2. Only NSCollectionViewFlowLayout seems to be capable of telling `NSCollectionView` to not scroll vertically (inspiration from here)All of this works smoothly, however: I'm now trying to implement drag & drop reordering of the items. This also works, but I noticed that the inter item gap indicator (blue line) is not being displayed properly, even though I do return proper sizes. I calculate them as follows:override func layoutAttributesForInterItemGap(before indexPath: IndexPath) -> NSCollectionViewLayoutAttributes? { var result: NSCollectionViewLayoutAttributes? = nil // The itemLayoutAttributes dictionary is created in prepare() and contains // the layout attributes for every item in the collection view if indexPath.item < itemLayoutAttributes.count { if let itemLayout = itemLayoutAttributes[indexPath] { result = NSCollectionViewLayoutAttributes(forInterItemGapBefore: indexPath) result?.frame = NSRect(x: itemLayout.frame.origin.x - 4, y: itemLayout.frame.origin.y, width: 3, height: itemLayout.size.height) } } else { if let itemLayout = itemLayoutAttributes.reversed().first { result = NSCollectionViewLayoutAttributes(forInterItemGapBefore: indexPath) result?.frame = NSRect(x: itemLayout.value.frame.origin.x + itemLayout.value.frame.size.width + 4, y: itemLayout.value.frame.origin.y, width: 3, height: itemLayout.value.size.height) } } return result }Per documentation, the indexPath passed to the method can be between 0 and the number of items in the collection view including if we're trying to drop after the last item. As you can see, I return a rectangle for the inter item gap indicator that should be 3 pixels wide and the same height as an item is.While the indicator is displayed in the correct x-position with the correct width, it is only 2 pixels high, no matter what height I pass in.How do I fix this?NB: If I temporarily change the layout to NSCollectionViewFlowLayout the indicator displays correctly.I'm overriding the following methods/properties in NSCollectionViewFlowLayout:- prepare()- collectionViewContentSize- layoutAttributesForElements(in rect: NSRect) -> [NSCollectionViewLayoutAttributes]- layoutAttributesForItem(at indexPath: IndexPath) -> NSCollectionViewLayoutAttributes?- shouldInvalidateLayout(forBoundsChange newBounds: NSRect) -> Bool- layoutAttributesForInterItemGap(before indexPath: IndexPath) -> NSCollectionViewLayoutAttributes?