Tag materials to make them available to be applied to meshes.
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 with the name V[BALL], and tagging two materials V[BLUE] and V[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.
Tags can only contain numbers, letters and the underscore ‘_’ character.
Take care to tag the material name itself, not a mesh the material is applied to or the textures that make up the material channels.