code: function(file, callback) {
        if (any(hook('loading', file), haveStopped)) return
        if ('readFile' in main)
          return readFile(file)
        else if (this.hasXhr()) {
          var request = this.xhr()
          request.open('GET', file, false)
          request.send(null)
          if (request.readyState == 4 && 
             (request.status == 0 || 
              request.status.toString().charAt(0) == 2)) 
            return request.responseText
        }
        else
          error("failed to load `" + file + "'")
      }
docs: Load a _file_'s contents.
  
  @param  {string} file
  @param  {function} callback
  @return {string}
  @api public