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.

return tagName.indexOf('-') >= 0 || props.is != null;
}
function setInitialDOMProperties(
  domElement: Element,
  rootContainerElement: Element,
  nextProps: Object,
  isCustomComponentTag: boolean,
): void {
  for (var propKey in nextProps) {
    var nextProp = nextProps[propKey];
    if (!nextProps.hasOwnProperty(propKey)) {
      continue;
    }
    if (propKey === STYLE) {
      if (__DEV__) {
        if (nextProp) {
          
          
          Object.freeze(nextProp);
        }
      }
      
      
      CSSPropertyOperations.setValueForStyles(domElement, nextProp);
    } else if (propKey === DANGEROUSLY_SET_INNER_HTML) {
      var nextHtml = nextProp ? nextProp[HTML] : undefined;
      if (nextHtml != null) {
        setInnerHTML(domElement, nextHtml);
      }
    } else if (propKey === CHILDREN) {