title: Query for field existence in CloudSearch
body: <p>Suppose I have an optional field called 'xyz' in the list of documents I've indexed in CloudSearch. </p>
  
  <p>How do I query CloudSearch so that it returns only those documents that contain 'xyz'?</p>
  
  <p>If I know up front, that it's a positive integer, I can probably do something like this to get the required list:
  <code>q=xyz:[0,}&amp;q.parser=structured</code></p>
  
  <p>But how do I do it if 'xyz' stores some other type like a string or a list of ints/strings etc.,?</p>
  
  <p>BTW, I've used Solr before, and there, I could simply do <code>q=xyz:*</code> to achieve this. Does CloudSearch support such regular expressions?</p>