3D models
Your own models from a file: .glb, .gltf, .fbx, .obj.
Importing
TODO: Describe the flow, including whether the file is copied or only referenced.
Size and orientation
TODO: The usual traps — models in centimetres, Z-up instead of Y-up.
Materials and textures
TODO: What is loaded along with the model and what is not.
As a prop on the avatar
A model can hang from a bone — but for a hat, a sword or a cup an accessory is usually the better route, because it brings physics with it.