json_schema: {
      "additionalProperties": false,
      "description": "A select_content GTM server-side event.",
      "properties": {
          "content_type": {
              "description": "The type of selected content.",
              "maxLength": 4096,
              "type": [
                  "string",
                  "null"
              ]
          },
          "item_id": {
              "description": "An identifier for the item that was selected.",
              "maxLength": 500,
              "type": [
                  "string",
                  "null"
              ]
          }
      },
      "self": {
          "format": "jsonschema",
          "name": "select_content",
          "vendor": "com.google.tag-manager.server-side",
          "version": "1-0-0"
      },
      "type": "object"
  }