URHO3D Open UI Layout default.xml

When you invoke the dafaultstyle.xml it oopens to the window that looks like a whole story board. I am wondering since I have looked at the angelscripts that are included with the engine.
Is it built into a script in the scripts directory or is that exact window built in source.

Could someone please point me the the source.cpp files if necessary?

Regards-

I did not understand your question. At all. Could you please be more specific?

The window on the top what is the source necessary to build this window? Is it just a few source.cpp files that run under something.as. In my UI Layout open Box. defaltstyles.xml open it up and I don’t have a clue off hand what way to reference this in my project yet.

Any help would be greatly appreciated.