This usually means that the user mixed up our lowercase/uppercase naming convention; see https://github.com/facebook/react/pull/3429#issuecomment-85166440.

We could add a message like

> Warning: The tag <commentBox> is unrecognized in this browser. If you meant to render a React component, start its name with an uppercase letter.

We'd check this only once per tag and only in development mode.

if (__DEV__) {
  var validatePropertiesInDevelopment = function(type, props) {
    validateARIAProperties(type, props);
    validateInputPropertes(type, props);
    validateUnknownPropertes(type, props);
  };
}
function ensureListeningTo(rootContainerElement, registrationName) {
  var isDocumentFragment = rootContainerElement.nodeType === DOC_FRAGMENT_TYPE;
  var doc = isDocumentFragment
    ? rootContainerElement
    : rootContainerElement.ownerDocument;
  listenTo(registrationName, doc);
}
var mediaEvents = {
  topAbort: 'abort',
  topCanPlay: 'canplay',
  topCanPlayThrough: 'canplaythrough',
  topDurationChange: 'durationchange',
  topEmptied: 'emptied',
  topEncrypted: 'encrypted',
  topEnded: 'ended',
  topError: 'error',
  topLoadedData: 'loadeddata',
  topLoadedMetadata: 'loadedmetadata',
  topLoadStart: 'loadstart',
  topPause: 'pause',
  topPlay: 'play',
  topPlaying: 'playing',
  topProgress: 'progress',