title: communicating between two separate Directives
body: <p>what is the best way to have two directives talk to each other? Lets say I have the following setup:</p>
  
  <pre><code>&lt;drop-uploader&gt;&lt;/drop-uploader&gt;
  &lt;drop-uploader&gt;&lt;/drop-uploader&gt;
  
  &lt;progress-bar&gt;&lt;/progress-bar&gt;
  </code></pre>
  
  <p>whats the best way to have the "uploader" directive notify the "progress bar" directive? Is the best way to use events on the rootScope or use a service? Is there a way to reference a directive as an attribute on another directive to access its scope? Something like this...</p>
  
  <pre><code>&lt;drop-uploader progress-bar="thisone"&gt;&lt;/drop-uploader&gt;
  &lt;drop-uploader progress-bar="thisone"&gt;&lt;/drop-uploader&gt;
  
  &lt;progress-bar name="thisone"&gt;&lt;/progress-bar&gt;
  </code></pre>