the window on which the data is stored
location to store a pointer to the retrieved data. If the retrieval failed, %NULL we be stored here, otherwise, it will be non-%NULL and the returned data should be freed with g_free() when you are finished using it. The length of the allocated memory is one more than the length of the returned data, and the final byte will always be zero, to ensure nul-termination of strings
location to store the type of the property
location to store the format of the property
the length of the retrieved data.
Retrieves selection data that was stored by the selection data in response to a call to gdk_selection_convert(). This function will not be used by applications, who should use the #GtkClipboard API instead.