SetterObservable's call a function when set. Their getter is backed up by an observation.
function SetterObservable(getter, setter) {
	this.setter = setter;
	this.observation = new Observation(getter);
	this.handler = this.handler.bind(this);

	//!steal-remove-start
	if (process.env.NODE_ENV !== 'production') {
		canReflect.assignSymbols(this, {
			"can.getName": function() {
				return (
					canReflect.getName(this.constructor) +
					"<" +
					canReflect.getName(getter) +
					">"
				);
			}
		});
		Object.defineProperty(this.handler, "name", {
			value: canReflect.getName(this) + ".handler"
		});
	}
	//!steal-remove-end
}