Collection Reusable Views, including Collection View Cells (which is a subclass), have a field in Interface Builder called "Identifier" with prompt "Reuse Identifier".

However, you normally use it by registering it with the `UICollectionView` using the `–registerNib:forCellWithReuseIdentifier:` and `–registerNib:forSupplementaryViewOfKind:withReuseIdentifier:` methods, where you also specify a reuse identifier.

So then what's the point of setting one in Interface Builder? It seems to make no difference whether you set it there or not.