json_schema: {
      "$schema": "http://json-schema.org/draft-04/schema#",
      "title": "crs",
      "description": "a Coordinate Reference System object",
      "type": [
          "object",
          "null"
      ],
      "required": [
          "type",
          "properties"
      ],
      "properties": {
          "type": {
              "type": "string"
          },
          "properties": {
              "type": "object"
          }
      },
      "additionalProperties": false,
      "oneOf": [
          {
              "$ref": "#/definitions/namedCrs"
          },
          {
              "$ref": "#/definitions/linkedCrs"
          }
      ],
      "definitions": {
          "namedCrs": {
              "properties": {
                  "type": {
                      "enum": [
                          "name"
                      ]
                  },
                  "properties": {
                      "required": [
                          "name"
                      ],
                      "additionalProperties": false,
                      "properties": {
                          "name": {
                              "type": "string",
                              "FIXME": "semantic validation necessary"
                          }
                      }
                  }
              }
          },
          "linkedObject": {
              "type": "object",
              "required": [
                  "href"
              ],
              "properties": {
                  "href": {
                      "type": "string",
                      "format": "uri",
                      "FIXME": "spec says \"dereferenceable\", cannot enforce that"
                  },
                  "type": {
                      "type": "string",
                      "description": "Suggested values: proj4, ogjwkt, esriwkt"
                  }
              }
          },
          "linkedCrs": {
              "properties": {
                  "type": {
                      "enum": [
                          "link"
                      ]
                  },
                  "properties": {
                      "$ref": "#/definitions/linkedObject"
                  }
              }
          }
      }
  }