Pega Platform applications use a modular UI which encourages prototyping, and design consistency. You can reuse out-of-the-box UI components, group them into structural clusters, or nest one component inside another.

For portals, the most basic structural component is the harness. Harnesses organize the structure of the user display. When you create a portal in App Studio, Pega Platform automatically creates an associated harness to contain the screen layout. If you design your portal in Dev Studio, you must manually create a harness and associate it with a portal.

The harness contains one screen layout that is divided further into sections. Each section in the screen layout defines the content of one part of a user interface, such as the navigation pane or a header. You can populate a section with properties and controls, and choose a template to organize the section in a consistent manner. Like harnesses, sections are reusable and support nesting – you can embed a section inside another section.