Optional thumbnail image inside .glb file

Provide an option to have an embedded thumbnail file (.png or .jpg) in the .glb file.
Windows Explorer can then show that thumbnail, making it easier to find assets on disk.

Ideally the **.glb** file would just be a **.zip** format file so you could store **thumbnail.png** inside the file, together with other information like the author, etc. They would just go along with the .glb (.zip format) file.

If we're too late to make .glb a .zip file, how about we create a new file extension, **.glz** that is a .zip format file containing the **.gltf,** any **textures** in their original file format inside the .zip, etc. It would be exactly the same as the current .zip file that we can download from _SketchFab_ but with the .glz extension and optionally containing a thumbnail.png file.

Start by comparing the proposed .glb embedding approach with the alternative .glz archive containing a .gltf file, original textures, and an optional thumbnail.png. The issue names no repository files or tests; done would require an agreed format direction and the corresponding specification changes.

Written by the indexing model from the issue text.