Tag materials to make them available to be applied to meshes. Use swatches to ensure your materials aren't removed when exporting.
When you tag a material with a name, you make that material available to be applied to any tagged mesh. For example by tagging a mesh named BALL, and tagging two materials BLUE and RED, you allow viewers to request the BALL with either the RED or BLUE material applied.
You only need to tag materials you want to be available for applying to tagged meshes. Think of these tagged materials as a paint pallet you can then use on any meshes in the model. If you don't want to swap any materials, you don't need to tag them.
Warning: Take care to tag the material name itself, *not* a mesh the material is applied to.
Chances are, you'll have many more materials than meshes, and most 3D editors will remove unused materials when exporting. To ensure your GLTF file includes all the materials you have tagged, we create ‘swatches’ for each material in the file.
A swatch is just a tiny mesh you tag with V[SWATCH], then apply a material to, guaranteeing the material is then available to generate variants. Swatches won't be tagged with anything else (like a tag-name), as they are just a delivery method for your tagged materials.