What about a "Magic Theory" tag for novels that go into depth about the magic system in the world; "System" magic where magic aptitude and activation is controlled by a game-like system won't count, unless the "System" is more of a lassiez-faire approach and doesn't interfere much in controlling the magic for the user, like in Chrysalis at RoyalRoad, where the System just gives basic knowledge of magic and it's up to the user to know how to apply it.