The files with the xprj extension are project files for the Epeios software. They are in XML format, with namespace http://zeusw.org/epeios/xprj (xmlns=”http://zeusw.org/epeios/xprj”).
Each software has is own set of recognized tags, but all have the root tag Projects, enclosing a Project tag with a target attribute which value is the name of the software.
You can also use the xpp directives (which must currently belongs to xpp namespace).