observe-callback
Domain: Jupyter Integration
🎯 Motivation
A method triggered when a widget’s trait changes. Register it with widget.observe(handler, names='value').
📋 Concrete Example
Call slider.observe(on_change, names='value') so on_change(change) fires whenever the slider moves.
🔗 Analogy
An observe callback is a motion sensor light — when the widget value moves, your function turns on.