title: Purpose of @ in ERB templates
body: <p>I've frequently seen code like this in ERB templates:</p>
  
  <pre><code>&lt;%= @some_variable %&gt;
  </code></pre>
  
  <p>And seen code like this:</p>
  
  <pre><code>&lt;%= node[:some_attribute][:some_other_attribute] %&gt;
  </code></pre>
  
  <p>And just plain old</p>
  
  <pre><code>&lt;%= some_variable %&gt;
  </code></pre>
  
  <p>Is there a difference?  Should I be concerned?</p>