Generally, Raw Development data (not the published/compiled files)
Should base on some generic fileformat.
XML is perfect for such description-tasks like a level.

Its easily extentable (furure proof), and offers the option to manually edit
the data.
(for example switching all textureA with TextureB, or changing file-paths, just
using a simple text-editor replace.)

The user ist not required to understand xml, when WED
uses it.