docs: function() {
      var self = this;
  
      // Get the Howl we want to manipulate.
      var sound = self.playlist[self.index].howl;
  
      // Determine our current seek position.
      var seek = sound.seek() || 0;
      timer.innerHTML = self.formatTime(Math.round(seek));
      progress.style.width = (((seek / sound.duration()) * 100) || 0) + '%';
  
      // If the sound is still playing, continue stepping.
      if (sound.playing()) {
        requestAnimationFrame(self.step.bind(self));
      }
    }