test.schema.json

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "selections": {
      "type": "array",
      "items": {
        "oneOf": [
          {
            "type": "string"
          },
          {
            "$ref": "#/definitions/objectDef"
          }
        ]
      }
    },
    "other": {
      "type": "array",
      "items": {
        "$ref": "#/definitions/objectDef"
      }
    }
  },
  "required": ["selections"],
  "definitions": {
    "objectDef": {
      "type": "object",
      "properties": {
        "value": { "type": "string" }
      }
    }
  }
}