code: function advance() {
  	const start = now();
  	config.depth = ( config.depth || 0 ) + 1;
  
  	while ( config.queue.length && !config.blocking ) {
  		const elapsedTime = now() - start;
  
  		if ( !defined.setTimeout || config.updateRate <= 0 || elapsedTime < config.updateRate ) {
  			if ( priorityCount > 0 ) {
  				priorityCount--;
  			}
  
  			config.queue.shift()();
  		} else {
  			setTimeout( advance, 13 );
  			break;
  		}
  	}
  
  	config.depth--;
  
  	if ( !config.blocking && !config.queue.length && config.depth === 0 ) {
  		done();
  	}
  }
docs: Advances the ProcessingQueue to the next item if it is ready.
  @param {Boolean} last