title: @internal JavaScript documentation tag inside react code, is this jsdoc, closure, or something else?
body: <p>I noticed that React uses the <code>@internal</code> tag for documentation.  What program consumes this tag?  Is it jsdoc or something else?  Google Closure Compiler?  I can't find this tag on <a href="http://usejsdoc.org/" rel="noreferrer">http://usejsdoc.org/</a> or in the Google Closure Compiler documentation.  What is it used for?</p>
  
  <p>Here is an example -</p>
  
  <pre><code>/**
   * Warn for mutations.
   *
   * @internal
   * @param {object} object
   * @param {string} key
   */
  function defineWarningProperty(object, key) {
  </code></pre>
  
  <p><a href="https://github.com/facebook/react/blob/master/src/classic/element/ReactElement.js" rel="noreferrer">https://github.com/facebook/react/blob/master/src/classic/element/ReactElement.js</a></p>