From the internal tags description of the RH Topic Tags extension:
Allowed tags: -, 0-9, a-z, A-Z, spaces (will be converted to -), min: 3, max: 30
Special case Skyrim:
Skyrim and its different versions and variants are bundled in the "The Elder Scrolls V - Skyrim" discussion hub. You can use the "Skyrim-Classic"* and "Skyim-SE"** tags to differentiate between the different versions.
* 32-bit Skyrim, also called Oldrim, including the Legendary Edition variant
** 64-bit Skyrim, also called Special Edition, including the Anniversary Edition variant