If the clipboard contents callbacks were set with gtk_clipboard_set_with_owner(), and the gtk_clipboard_set_with_data() or gtk_clipboard_clear() has not subsequently called, returns the owner set by gtk_clipboard_set_with_owner().
the owner of the clipboard, if any; otherwise %NULL.
See Implementation
If the clipboard contents callbacks were set with gtk_clipboard_set_with_owner(), and the gtk_clipboard_set_with_data() or gtk_clipboard_clear() has not subsequently called, returns the owner set by gtk_clipboard_set_with_owner().