Summary: Containership is a useful interaction design technique that can help you direct your user's attention and shape their experience by giving them visual boundaries. Containership indicates a separation of controls or navigation in an activity space so users know there is a control and it lives in relationship to that section or sub-section of your site or app.
The deliberate use of containership can improve your user experience. It can give users intuitive cues either visually or through proximity and hierarchy.
What is "containership"?
Containership is a visual grouping technique that shows spatial relationship of similar items or actions. Visually shaded areas contain the icon, information, or action a user is expected to perform.
Think of containership as the curbside of a road (the curb contains the road) or the edging of a garden (the edging contains the flowers).