code: function(text, root, callback) {
        var matches = this.extractUrls(text, root);
  
        // every call to process returns all the text this loader has ever received
        var done = callback.bind(null, this.map);
        this.fetch(matches, done);
      }
docs: take a text blob, a root url, and a callback and load all the urls found within the text returns a map of absolute url to text