title: What does msg mean in Mirth?
body: <p>I'm trying to learn my way around some Mirth code. I keep seeing things like this in the transformer for different channels:</p>
  
  <pre><code>msg['PRB']['PRB.4']['PRB.4.2'].toString()
  </code></pre>
  
  <p>I understand that this is parsing a HL7 message and I understand that msg probably means message. But is <code>MSG</code> a system-wide variable? Does every channel have a <code>msg</code> variable? What is the scope of <code>msg</code>? I also keep seeing things like <code>${message.encodedData}</code> in the Templates. Do certain connector types automatically send the contents of <code>msg</code>?</p>