title: Cross Group (XG) Transactions and Further Explanation of use
body: <p>The <a href="http://googleappengine.blogspot.com/2011/10/app-engine-155-sdk-release.html" rel="nofollow">most recent release</a> of the GAE states the following changes:</p>
  
  <blockquote>
    <p><strong>Datastore</strong></p>
    
    <p>Cross Group (XG) Transactions: For those who need transactional writes
    to entities in multiple entity groups (and that's everyone, right?),
    XG Transactions are just the thing. This feature uses two phase commit
    to make cross group writes atomic just like single group writes.</p>
  </blockquote>
  
  <p>I think I could use this change within the code of a project I created a while ago but I would like further information regarding this update to the App Engine.  I can't seem to find any additional information.  So...</p>
  
  <p>How has coding transactions changed, in regards to this update?  In layman's terms, how can I implement a cross-group transaction and are there still some limitations to data store transactions that I need to be aware of?</p>
  
  <p>I know this is a rather vague question.  My problem is that this sounds very useful, but I'm not sure how to correctly (and effectively) use this change.</p>