json_schema: {
      "$schema": "http://json-schema.org/draft-04/schema#",
      "type": "object",
      "properties": {
          "email": {
              "type": "string",
              "format": "email",
              "maxLength": 1024
          },
          "relativeTo": {
              "oneOf": [
                  {
                      "type": "string"
                  },
                  {
                      "type": "number"
                  },
                  {
                      "type": "object",
                      "properties": {
                          "$date": {
                              "type": "string"
                          }
                      },
                      "additionalProperties": false,
                      "required": [
                          "$date"
                      ]
                  }
              ]
          },
          "templateContext": {
              "type": "string",
              "maxLength": 32767
          }
      },
      "additionalProperties": false
  }