code: function(force) {
        // Prevent FF from raising an error when it is firing timeouts
        // on a page that's no longer loaded.
        if (!window.select) return;
  
        if (!this.options.readOnly) select.markSelection(this.win);
        var start, endTime = force ? null : time() + this.options.passTime;
        while ((time() < endTime || force) && (start = this.getDirtyNode())) {
          var result = this.highlight(start, endTime);
          if (result && result.node && result.dirty)
            this.addDirtyNode(result.node);
        }
        if (!this.options.readOnly) select.selectMarked();
        if (start) this.scheduleHighlight();
        return this.dirty.length == 0;
      }
docs: Pick dirty nodes, and highlight them, until options.passTime milliseconds have gone by. The highlight method will continue to next lines as long as it finds dirty nodes. It returns information about the place where it stopped. If there are dirty nodes left after this function has spent all its lines, it shedules another highlight to finish the job.