JED 1.6.0+ - Simple flat dimension with normal biomes

{
    "dimensions": [
        {
            "dim": 123,
            "normal_biomes": true,
            "dimensiontype": {
                "id": 123,
                "name": "Flat",
                "worldprovider": "WorldProviderSurfaceJED",
                "require_exact_match": true
            },
            "worldinfo_onetime": {
                "generatorName": "flat",
                "generatorOptions": "3;1*minecraft:bedrock,62*minecraft:dirt,1*minecraft:grass;1;"
            }
        }
    ]
}