After a discussion about the evolution of the .sh3d format with some French experts, it seemed better that the Home.xml uses some XML elements and attributes close to the classes of the model layer, rather than an existing XML format like Collada or BIM XML. Just open a Home.xml and you'll recognize the data handled by Sweet Home 3D classes. I don't dream of creating a new standard, but at least this should help to exchange data with other programs if needed.