title: How can I add a title/label supplementary view for each cell in a UICollectionViewFlowLayout?
body: <p>All examples I've seen use the supplementary view as headers or footers. I need to add a label above and/or below each cell in my flow layout.</p>
  
  <p>At first I thought all I had to do was <em>register a class for a supplementary view of kind</em> and then implement <em>collectionViewForSupplementaryElementOfKindAtIndexPath</em> and I'd be good to go, but it seems <em>FlowLayout</em> out of the box only supports headers and footers.</p>
  
  <p>The apple docs seems to suggest anything more will require a subclassing effort of <em>FlowLayout</em>.</p>
  
  <p>Since I don't want to rework the work apple has done for flow layout and since my cells are expected to differ in size, I'd like to extend Flow Layout to support a supp view per cell.</p>
  
  <p>I'm thinking I should be able to accomplish this by subclassing UICollectionViewFlowLayout.</p>
  
  <p>But I'm not sure how to tell the flow layout to ask for a supplementary view for each cell.
  Simply registering a class for the supp view does not force the layout to invoke <em>layoutAttributesForSupplementaryViewOfKind</em>. As it stands, that is never called in my subclass. I figured if i reg a class for a supp view, it should ask for the sup view for each of the items in my section... this seems to be an incorrect assumption.</p>
  
  <p>I've seen a great custom layout example where the layout was manually managed using NSDictionaries but I'm not sure how to apply that knowledge to the built-in flow layout.</p>