Anyone immediately understands how to set an extrema.
These buttons could have the appearance of those found at the edge of the scrollbars, the scroll arrows.
(as little triangle black/white with the point indicating towards the outside of the slider)
but then taking into account a margin of imprecision of the click !
Let’s say, for example, a 10% right click in the slider sets the maximum value (resp. left and minimum value).
On the other hand, looking at the slider, the user has no idea of the extension of the behavior of the slider when facing a left… or right click.
Might be nice to have Shift+click to move the slider to the nearest, e.g. 10% increment between the min & max. That would allow a quick & dirty way of setting options reproducibly between ParaView view panels & GUI instances.
Another useful trait would be to show the exact current slider value on mouseover