http://www.minecraftforum.net/topic/1753435-14715-just-another-spawner-jas-v082/page__st__340#entry22786652

Sort of like BiomeGroups; some immutable and some user configurable. Can be added to biomegroups identically to BiomeGroups (separating names by commas).

Unlike BiomeGroups, they would not generate entries in Entities, allows groups of biomes to be maintained without spamming Entity CFGs with useless entries.

Each BiomeDictionary entry should be an immutable attribute.

Closed via a2458de

This also introduces the ability to add and subtract mappings and attributes when used in biomegroups by prefixing a + or - in front of them. (Default assumes +)