Historical Rules · 26 August 2016
Rule 309.3
Official source text from the 26 August 2016 Rules release
Plane subtypes are listed after a long dash, and may be multiple words: “Plane — Serra’s Realm.” All words after the dash are, collectively, a single subtype. Planar subtypes are called planar types. A plane can have only one subtype. See rule 205.3n for the complete list of planar types.