code: function update(prop) {
      // trigger change if necessary
      if (!deepEqual(cache[prop], _get(prop))) {
        trigger('change', prop);
      }
      // Notify dependents
      (deps[prop] || []).forEach(function(dep) {
        delete children[dep[0]];
        dep[1].trigger('update', dep[0]);
      });
      // Notify computed properties, depending on parent object
      if (instance.parent) {
        instance.parent.trigger('update', instance.prop);
      }
    }
docs: Update handler