code: function getEnv() {
      var ua = navigator.userAgent;
  
      env = {
        // True if this browser supports disabling async mode on dynamically
        // created script nodes. See
        // http://wiki.whatwg.org/wiki/Dynamic_Script_Execution_Order
        async: doc.createElement('script').async === true
      };
  
      (env.webkit = /AppleWebKit\//.test(ua))
        || (env.ie = /MSIE/.test(ua))
        || (env.opera = /Opera/.test(ua))
        || (env.gecko = /Gecko\//.test(ua))
        || (env.unknown = true);
    }
docs: Populates the <code>env</code> variable with user agent and feature test
  information.
  
  @method getEnv
  @private