title: Google Cloud Messaging: Can you send to a select group of users?
body: <p>For a project we need to send push notifications to the user when he/she is expected to fill in some values in our app. I thought about Google Cloud Messaging. However, we will have several locations where the user can be, and only the user in a specific location needs to receive the message.</p>
  
  <p>I see no option in GCM to register with optional variables like "location:6". So, is it possible to group devices/users based on a supplied variable? Or is it only useful for sending notifications to all registered users? If so, are there alternatives?</p>