code: function schedule(fn) {
  		// Add or replace.
  		nextBatch[ tag(fn) ] = fn;
  		// Request only if needed.
  		if (!pendingFrame) {
  			pendingFrame = true;
  			requestAnimationFrame(frame);
  		}
  	}
docs: Rendering and scheduling ------------------------ /*
  Queues a handler for execution in the next batch, then
  requests a frame, unless already requested. Replaces all
  previous schedules for this handler or any other handler
  with the same tag.