Basic behavior for between reusableView and contentView.

<b>UICollectionReusableView</b>
It's behavior define class for reusableView in UICollectionView.
Typically, Use for header, footer view. and not have backgroundView and contentView.

<b>UICollectionViewCell</b>
It's subclass from UICollectionReusableView.

One big different thing is, it's have backgroundView and contentView.
contentView is above backgroundView, and all subviews have to add to contentView not cell itself.

UICollectionViewCell's contentView isn't predefined in Interface builder.
but, UICollectionViewCell is automatically added all view what you defined to contentView when initiate.

<b>UITableViewHeaderFooterView</b>
It's not provided from Interface builder, can only initiate by code.
Have backgroundView and contentView and have to register to tableView manually.

<b>UITableViewCell</b>
almost same with UICollectionViewCell, also have backgroundView and contentView.
Even has more views like sepatatorView and UIButton.
UITableViewCell's contentView is predefined in Interface builder.