CEGUI In Practice - Using .layout files
From CEGUI Wiki - Crazy Eddie's GUI System (Open Source)
CEGUI InPractice 5
In this tutorial we will introduce how to use the .layout file. This is likely what will be used for larger scale projects, where the art team isn't going to want to wait for you to recompile the source for every change they make.
Meet the Layout
The Layout file (.layout) is an xml file. There exists at least two editors for layouts. the first one is the CEGUI LayoutEditor