Tooltips for sliders

[aplavin]

The title says it all: basically, often it would be quite useful to have tooltips when hovering over a slider, with these tooltips showing the value (or label for selection slider) which will be selected if clicking at this point.

[jasongrout]

It would be easy to implement a tooltip for the slider handle. I think it would be hard to implement a tooltip over the slider track (though maybe not impossible).