How are live tiles made in Windows 8?

Finally figured it out, these live tiles are using tile notifications as noted by others.

Here is the minimal code necessary for updating an existing default tile with a template:

1. You have to load in a template and adjust it, or produce your own XML code. See the tile schema…

   var tileXml = Notifications.TileUpdateManager.getTemplateContent(template); 
   

2. You need to create a notification, which apparently is an update to a tile.

   var notification = new Notifications.TileNotification(tileXml); 
   

3. You need to create an updater, which will provide you with methods to notify through your tile.

   var upd = Notifications.TileUpdateManager.createTileUpdaterForApplication();
   

4. If you have all this, you can send an update to the client.

   upd.update(notification);