definitions/feature_rules/overworld_surface_kelp_feature.json

{
  "format_version": "1.13.0",
  "minecraft:feature_rules": {
    "description": {
      "identifier": "minecraft:overworld_surface_kelp_feature",
      "places_feature": "minecraft:kelp_feature"
    },
    "conditions": {
      "placement_pass": "surface_pass",
      "minecraft:biome_filter": [
        // (overworld && !ocean) || (ocean && (warm || (frozen && monster)))
        {
          "any_of": [
            {
              "all_of": [
                {
                  "any_of": [
                    {
                      "test": "has_biome_tag",
                      "operator": "==",
                      "value": "overworld"
                    },
                    {
                      "test": "has_biome_tag",
                      "operator": "==",
                      "value": "overworld_generation"
                    }
                  ]
                },
                {
                  "test": "has_biome_tag",
                  "operator": "!=",
                  "value": "ocean"
                }
              ]
            },
            {
              "all_of": [
                {
                  "test": "has_biome_tag",
                  "operator": "==",
                  "value": "ocean"
                },
                {
                  "any_of": [
                    {
                      "test": "has_biome_tag",
                      "operator": "==",
                      "value": "warm"
                    },
                    {
                      // frozen_ocean should receive this kelp feature, but legacy_frozen_ocean
                      // should not. The only distinguishing tag between the two is "monster",
                      // which is only present on frozen_ocean
                      "all_of": [
                        {
                          "test": "has_biome_tag",
                          "operator": "==",
                          "value": "frozen"
                        },
                        {
                          "test": "has_biome_tag",
                          "operator": "==",
                          "value": "monster"
                        }
                      ]
                    }
                  ]
                }
              ]
            }
          ]
        }
      ]
    },
    "distribution": {
      "iterations": 0, // most biomes no-op, but we still need to roll our scatter chance to keep rand consistent
      "scatter_chance": {
        "numerator": 1,
        "denominator": 18
      },
      "x": 0,
      "y": 0,
      "z": 0
    }
  }
}