Several Mac apps, both Apple and third-party, have a menu in the left column, usually used to filter content. Below are some examples from iPhoto, iCal, and iTunes.
I do not see the interface constructor class that matches this. How are they usually implemented? NSTableView with custom cells? Is there pre-written code to handle more complex aspects such as folding triangles? It looks like such a common user interface that I don't want to reinvent the wheel if I don't need it.
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