NSCollectionViewSectionHeaderView
A protocol that defines a button to control the collapse of a collection view’s section.
Declaration
protocol NSCollectionViewSectionHeaderView : NSCollectionViewElementOverview
A collection view can support a section that can collapse into a single horizontally scrollable row, similar to the groupings in the icon view in Finder. To ensure that the collection view can communicate with the button that controls the collapsing of a section, the section header view object should conform to this protocol and connect the button’s outlet to sectionCollapseButton.