title: What is the purpose of Thrift parameter numbering?
body: <p>What is the purpose of the numbers before each parameter (field identifiers)? Why does it jump from 5 to 16?</p>
  
  <pre><code>struct Tweet {
      1: required i32 userId;
      2: required string userName;
      3: required string text;
      4: optional Location loc;
      5: optional TweetType tweetType = TweetType.TWEET;
      16: optional string language = "english";
  }
  </code></pre>
  
  <p>(Snippet from <a href="http://diwakergupta.github.io/thrift-missing-guide/" rel="noreferrer">http://diwakergupta.github.io/thrift-missing-guide/</a>)</p>
  
  <p>I've been trying to find the answer to this for a while and haven't found anything in the docs.</p>