It seems problematic to allow arbitary non-lowercase attribute on HTML nodes. Because the server has no ability to keep them case sensitive (HTML isn't). So they will end up different on the client.

We should probably warn if the attribute is not a known one *and* is not lowercase.
return expectErrors(async () => {
    ExecutionEnvironment.canUseDOM = true;
    await asyncReactDOMRender(reactElement, domElement, forceHydrate);
    ExecutionEnvironment.canUseDOM = false;
    return domElement.firstChild;
  }, errorCount);
}
async function renderIntoString(reactElement, errorCount = 0) {
  return await expectErrors(
    () =>
      new Promise(resolve =>
        resolve(ReactDOMServer.renderToString(reactElement)),
      ),
    errorCount,
  );
}
async function serverRender(reactElement, errorCount = 0) {
  const markup = await renderIntoString(reactElement, errorCount);
  var domElement = document.createElement('div');
  domElement.innerHTML = markup;
  return domElement.firstChild;
}
class DrainWritable extends stream.Writable {