Doomsday 2 manages resources as assets. In practice, an asset is comprised of Doomsday Script and a set of associated files inside a package.
Before you start working with assets, you should have a good understanding of how packages work in Doomsday 2.
The asset system was first introduced in 1.15. It was only used for the GL2 model renderer.
In 2.0, assets were added for particle texture images and 3D model reflection cube maps.