gtkClipboardRequestContents: gtkClipboardRequestContents
In RGtk2: R Bindings for Gtk 2.8.0 and Above

Requests the contents of clipboard as the given target. When the results of the result are later received the supplied callback will be called.

1	gtkClipboardRequestContents(object, target, callback, user.data = NULL)

`object`	a `GtkClipboard`
`target`	an atom representing the form into which the clipboard owner should convert the selection.
`callback`	A function to call when the results are received (or the retrieval fails). If the retrieval fails the length field of `selection.data` will be negative.
`user.data`	user data to pass to `callback`