title: create-react-app (TypeScript) .babelrc throwIfNamespace=true setting
body: <p>thought this would be simple but it's not.  I generated a simple app with the latest create-react-app.  Adding  a <code>&lt;gcse:search&gt;</code> tag and getting the following:</p>
  
  <pre><code>Namespace tags are not supported by default. React's JSX doesn't support namespace tags. You can turn on the 'throwIfNamespace' flag to bypass this warning.
    16 |         return (
    17 |             &lt;div className="comptext"&gt;
  &gt; 18 |                 &lt;gcse:search defaultToRefinement="mostly-center"&gt;&lt;/gcse:search&gt;
       |                  ^
    19 |             &lt;/div&gt;
    20 |         );
  </code></pre>
  
  <p>.babelrc is:</p>
  
  <pre><code>{
      "presets": [
          [
              "@babel/preset-react",
              {
                  "throwIfNamespace": false
              }
          ]
      ]
  }
  </code></pre>
  
  <p>I've tried multiple .babelrc configurations, "babel" key in package.json, even tried including .bablerc.js.  No change</p>
  
  <p>I'd prefer to not eject this, if possible.</p>
  
  <p>What am I missing?</p>