BookmarkKit 
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It provides a basic storage for shared bookmarks.
It can be used for web browser bookmark, recently opened documents, etc.
It is based on CollectionKit.

BookmarkKit has a basic assumption: it has a hierarchical structure.
A bookmark or a group can only exist under a group.
In another word, an item or a group can has a parent or none.
Therefore, bookmark can be displayed in NSOutlineView.


