JSON Schema Draft-07 schema For dynamic keys in an enum

Is there way to define a draft-07 JSON Schema for keys that are not predefined but, each key is constrained to an enum? The json sample will look like:

{
    "letters": {
        "a": [1, 2, 3],
        "b": [2, 3]
    }
}

Where keys in the letters object are constrained by an enum: key in ["a", "b", "c"].

I want to be able to use any number of keys as long as they are in the enum such that the following json can also pass:

{
    "letters": {
        "a": [1, 2, 3],
    }
}

keys that are not predefined but each key is constraint to an enum

use additionalProperties to create an object schema constrained to an enum with dynamic properties

{
  "type": "object",
  "properties": {
    "letters": {
      "type": "object",
      "additionalProperties": {
          "enum": [1,2,3]
      }
    }
  }
}

---

This will validate

{
  "letters": {
    "a": 2,
    "ddd": 1
  }
}

---

Where keys in the letters object are constraint by an enum: key in ["a", "b", "c"].

I want to be able to any number of keys as long as they are in the enum

The keyword(s) which may work are patternProperties or propertyNames .

{
  "type": "object",
  "properties": {
    "letters": {
      "patternProperties": {
        "a|b|c": {
          "enum": [1,2,3]
        }
      }
    }
  }
}

--

This would validate

{
  "letters": 
    "a": 1,
    "b": 2, 
    "c": 3
}

OR

This one can be tricky because an enum can define any JSON Schema schema, such as: boolean, number, integer, null, object, or array. These are invalid JSON property(key) names. Only string schemas SHALL be defined in propertyNames enumeration.

{
  "type": "object",
  "properties": {
    "letters": {
      "propertyNames": {
        "enum": ["a","b","c"]
      },
      "additionalProperties": {
        "enum": [1,2,3]
      }
    }
  }
}

---

This would validate.

{
  "letters": {
    "a": 1,
    "b": 2,
    "c": 3
  }
}

If you want the values to be an array of numbers, you should modify the additionalProperties schema to

"additionalProperties": {
  "type": "array",
  "items": [{"type": "number"]}
}

---

This would validate

{
    "letters": {
        "a": [1, 2, 3]
    }
}