an atom representing the form into which the clipboard owner should convert the selection.
a newly-allocated #GtkSelectionData object or %NULL if retrieving the given target failed. If non-%NULL, this value must be freed with gtk_selection_data_free() when you are finished with it.
Requests the contents of the clipboard using the given target. This function waits for the data to be received using the main loop, so events, timeouts, etc, may be dispatched during the wait.