Return the contents of the current X selection. The keyword argument selection names the selection and defaults to PRIMARY. The keyword argument type specifies the form in which the data is to be returned (the desired conversion target), an atom name such as 'STRING' or 'FILE_NAME'; it defaults to STRING, except on X11, where UTF8_STRING is tried first and STRING is used as a fallback. The displayof keyword argument names a widget that determines the display from which to retrieve the selection, and defaults to this widget.