json_schema: {
      "$schema": "http://json-schema.org/draft-04/schema#",
      "title": "Constraint",
      "description": "Constraint to the parameter.",
      "type": "array",
      "items": {
          "type": "object",
          "required": [
              "allowed_pattern",
              "description"
          ],
          "properties": {
              "allowed_pattern": {
                  "description": "A regular expression pattern.",
                  "type": "string",
                  "default": "null"
              },
              "description": {
                  "description": "A human readable description of the constraint.",
                  "type": "string",
                  "default": "null"
              }
          }
      }
  }