nsIClipboard Interface

 This empties the clipboard and notifies the clipboard owner.
 This empties the "logical" clipboard. It does not clear the native clipboard.

 @param  aWhichClipboard Specifies the clipboard to which this operation applies.
 @result NS_OK if successful.

void emptyClipboard(in long aWhichClipboard)

 Given a transferable, get the clipboard data.

 @param  aTransferable The transferable
 @param  aWhichClipboard Specifies the clipboard to which this operation applies.
 @result NS_Ok if no errors

void getData(in nsITransferable aTransferable, in long aWhichClipboard)

 This provides a way to give correct UI feedback about, for instance, a paste 
 should be allowed. It does _NOT_ actually retreive the data and should be a very
 inexpensive call. All it does is check if there is data on the clipboard matching
 any of the flavors in the given list.

 @aFlavorList - nsISupportsCString's in a nsISupportsArray (for JavaScript).
 @param  aWhichClipboard Specifies the clipboard to which this operation applies.
 @outResult - if data is present matching one of 
 @result NS_OK if successful.

boolean hasDataMatchingFlavors(in nsISupportsArray aFlavorList, in long aWhichClipboard)

 Given a transferable, set the data on the native clipboard

 @param  aTransferable The transferable
 @param  anOwner The owner of the transferable
 @param  aWhichClipboard Specifies the clipboard to which this operation applies.
 @result NS_Ok if no errors

void setData(in nsITransferable aTransferable, in nsIClipboardOwner anOwner, in long aWhichClipboard)

 Allows clients to determine if the implementation supports the concept of a 
 separate clipboard for selection.
 
 @outResult - true if 
 @result NS_OK if successful.

boolean supportsSelectionClipboard()