(From GNOME guidelines) A slider allows the user to quickly
select a value from a fixed, ordered range, or to increase or
decrease the current value. The control looks like the type of
slider that you might find on an audio mixing desk or a hi-fi's
graphic equalizer. Use a slider when: - Adjusting the value
relative to its current value is more important than choosing an
absolute value. For example, a volume control: the average user
will usually think about turning the volume up or down to make a
sound louder or quieter, rather than setting the peak output to
a specific decibel value. - It is useful for the user to control
the rate of change of the value in real time. For example, to
monitor the effects of a color change in a live preview window
as they drag the RGB sliders. - Label the slider with a text
label above it or to its left, using sentence capitalization.
Provide an access key in the label that allows the user to give
focus directly to the slider. - Mark significant values along
the length of the