Returns the list of pasteboard types supported directly by the receiver.
An array of NSString objects. This array is empty by default. Subclasses must override to return the list of pasteboard formats they support.
When creating a subclass of NSImageRep, override this method to return a list representing the supported pasteboard types. For example, the NSBitmapImageRep class implements code similar to the following for this method:
If your subclass supports the types supported by its superclass, you must explicitly get the list of types from the superclass and add them to the array returned by this method.