Hi Tommy van Aalst,
You can create your custom pluggable widget to achieve this.
PFB
https://docs.mendix.com/howto8/extensibility/create-a-pluggable-widget-one/
Thanks,
Vignesh S
There is no out-of-the-box error handling on slider, you could build it by yourself, by having a message show up based on conditional visibility or a dynamic class (if the slidervalue exceeds a certain number, add error)
This would need you to add your own conditional messages, however putting validation on the slider-value does give it the ‘has-error’-class, so you could try and use that in (s)css to give it an error indication