json_schema: {
      "title": "Visual Variable Legend Options",
      "type": "object",
      "$schema": "http://json-schema.org/draft-04/schema",
      "description": "Options available for the legend for visual variables.",
      "properties": {
          "customValues": {
              "type": "array",
              "items": {
                  "type": "number"
              }
          },
          "showLegend": {
              "type": "boolean",
              "description": "Indicates whether to show the color/size/opacity ramp in the legend."
          },
          "title": {
              "type": "string",
              "description": "The title of the legend."
          }
      }
  }