register() {
    if (arguments.length === 0) {
      return;
    }

    if (arguments.length === 1 && typeof arguments[0] === "object") {
      return this.registerThemes(arguments[0]);
    }

    if (arguments.length === 1 && typeof arguments[0] === "string") {
      return this.default(arguments[0]);
    }

    if (arguments.length === 2 && typeof arguments[1] === "string") {
      return this.registerUrl(arguments[0], arguments[1]);
    }

    if (arguments.length === 2 && typeof arguments[1] === "object") {
      return this.registerRules(arguments[0], arguments[1]);
    }
  }
Add themes to be used by a rendition
@param {object | Array<object> | string}
@example themes.register("light", "http://example.com/light.css")
@example themes.register("light", { "body": { "color": "purple"}})
@example themes.register({ "light" : {...}, "dark" : {...}})