What is boxed width?
DX8’s responsive grid system uses a series of containers, rows, and columns to lay out and align content. When configuring your responsive grid you can set a pixel width for each breakpoint. This is called the boxed width.
When you add a container to your layout, you can choose to make it Fluid width (100% of its parent) or Boxed width (The width defined within your responsive grid settings). The Boxed width is always aligned centrally within the browser viewport and can be used to create a defined width for your content or layout that is managed globally within your Responsive grid settings.