I put 2 widgets into a widget controller, one for layers and one for legend. For the Layers widget, I am allowing the users to reorder the layers. Because all the layers are grouped by categories, this "reorder layers" ability will also allow the a layer to be taken out of the group. So you could take 1 layer out, turn the group off and that layer would still be visible on the map. However, the legend widget does not honor what is visible. It still thinks that layer is in the group and if the group is off, it doesn't show in the legend list, but the layer is on and zoomed to visibility. This seems like a bug or maybe not allow users to take layer out of a group?