The preferred place to ellipsize the string.
The text will be ellipsized if the progress bar does not have enough room to display the entire string, specified as a `PangoEllipsizeMode`.
Note that setting this property to a value other than pango_ellipsize_none has the side-effect that the progress bar requests only enough space to display the ellipsis ("..."). Another means to set a progress bar's width is [ [email protected]_size_request].