http://www.astorm.ch/masapi/doc/2.0/ch/capi/net/CompositeMassLoader.html#addFile()
fileType:String (default = null) — The priority of the file (must be
an int). If not defined and the fileOrURL parameter is an Object, then
the priority of the file will be extracted from the attribute
'priority'. If no priority is specified, then the priority will be
0.
priority:Function (default = null) — The type of the file. If not
defined and the fileOrURL parameter is an Object, then the type will
be extracted from the attribute 'type'.