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.

var ReactDOMComponentFlags = require('ReactDOMComponentFlags');
var ReactDOMComponentTree = require('ReactDOMComponentTree');
var ReactDOMInput = require('ReactDOMInput');
var ReactDOMOption = require('ReactDOMOption');
var ReactDOMSelect = require('ReactDOMSelect');
var ReactDOMTextarea = require('ReactDOMTextarea');
var ReactInstrumentation = require('ReactInstrumentation');
var ReactMultiChild = require('ReactMultiChild');
var ReactServerRenderingTransaction = require('ReactServerRenderingTransaction');
var emptyFunction = require('fbjs/lib/emptyFunction');
var escapeTextContentForBrowser = require('escapeTextContentForBrowser');
var invariant = require('fbjs/lib/invariant');
var inputValueTracking = require('inputValueTracking');
var validateDOMNesting = require('validateDOMNesting');
var warning = require('fbjs/lib/warning');
var didWarnShadyDOM = false;
var Flags = ReactDOMComponentFlags;
var getNode = ReactDOMComponentTree.getNodeFromInstance;
var listenTo = ReactBrowserEventEmitter.listenTo;
var registrationNameModules = EventPluginRegistry.registrationNameModules;
var CONTENT_TYPES = {string: true, number: true};
var STYLE = 'style';
var HTML = '__html';
var RESERVED_PROPS = {
  children: null,
  dangerouslySetInnerHTML: null,
  suppressContentEditableWarning: null,
};
var DOC_FRAGMENT_TYPE = 11;
function getDeclarationErrorAddendum(internalInstance) {