{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "properties": {
    "myArray": {
      "contains": {
        "properties": {
          "itemType": {
            "const": "type A"
          }
        }
      },
      "items": {
        "properties": {
          "itemType": {
            "type": "string"
          }
        }
      },
      "maxContains": 1,
      "type": "array"
    }
  }
}