JED 1.6.0+ - Custom mining dimension

{
    "dimensions": [
        {
            "dim": 123,
            "dimensiontype": {
                "id": 123,
                "name": "Custom mining dimension",
                "keeploaded": false,
                "worldprovider": "WorldProviderSurfaceJED",
                "require_exact_match": true
            },
            "worldinfo_onetime": {
                "generatorName": "flat",
                "generatorOptions": "3;minecraft:bedrock,62*minecraft:stone,minecraft:grass;1;caves,decoration",
                "RandomSeed": ""
            },
            "chunkgenerator": "ChunkGeneratorFlatJED"
        }
    ]
}