Observed this on react@16.0.0-beta.5

```js
import React from 'react';
import { renderToString } from 'react-dom/server';

const B = () => 'b';

console.log(renderToString(<div>{'a'}<B />{'c'}</div>));
```

This renders as `<div data-reactroot="">a<!-- -->bc</div>`. If you try to hydrate this you'll get the error: Text content did not match. Server: "bc" Client: "b".
out += '\n';
      }
      out += innerMarkup;
    } else {
      children = toArray(props.children);
    }
    var frame = {
      domNamespace: getChildNamespace(parentNamespace, element.type),
      tag,
      children,
      childIndex: 0,
      context: context,
      footer: footer,
    };
    if (__DEV__) {
      frame.debugElementStack = [];
    }
    this.stack.push(frame);
    return out;
  }
}
module.exports = ReactDOMServerRenderer;