Accessor of the fill-level slot of the gtk-range class.
The gtk-range-fill-level slot access function gets the current position of the fill level indicator.
The (setf gtk-range-fill-level) slot access function sets the new position of the fill level indicator.
The "fill level" is probably best described by its most prominent use case, which is an indicator for the amount of pre-buffering in a streaming media player. In that use case, the value of the range would indicate the current play position, and the fill level would be the position up to which the file/stream has been downloaded.
This amount of prebuffering can be displayed on the range's trough and is themeable separately from the trough. To enable fill level display, use the gtk-range-show-fill-level function. The range defaults to not showing the fill level.
Additionally, it is possible to restrict the range's slider position to values which are smaller than the fill level. This is controller by the gtk-range-restrict-to-fill-level function and is by default enabled.