The Magnolia UI project version 6.x contains both the UI framework used in Magnolia 5.7 (referred to as Magnolia 5 UI) and the Magnolia 6 UI framework. You can use either framework.
Magnolia 5 UI
In Magnolia 6, Magnolia 5 UI has been relocated to the
magnolia-ui-framework-compatibility module. Many Magnolia apps still rely on this old framework. The fully qualified class names have not changed, which ensures runtime compatibility for older custom components based on the classes from the Magnolia 5 UI framework.
Magnolia 6 UI
In the Magnolia 6 UI framework, the core components of the UI are located in the
magnolia-ui-framework module inherited from Magnolia 5.7. The new
magnolia-ui-framework-jcr module is also part of Magnolia 6 UI.
For more information on the Magnolia 6 UI modules, refer to UI module.