All the layouts included with Interface Editor are generated from xml files stored in the installation directory:
The xml schema for Interface Editor layouts is included in this directory - open the file "layout.xsd". If you have any questions, please contact support.
You may add your own layouts to the following directory, which is created the first time Interface Editor launches:
Documents/Pharos/Interface Editor/Layouts
Interface Editor will automatically load your layouts the next time it is launched. You can also reload your layouts in the Layout page of the new page wizard.