**Do you want to request a *feature* or report a *bug*?**

Feature

**What is the current behavior?**

While server rendering React DOM and then hydrating with a different structure, React rightly warns that there are inconsistencies. But when I first saw these warnings I was not sure exactly what was going wrong.

Here are a few of the warnings I have been receiving:

```
Warning: Did not find a matching <button> in <div>.

Warning: Did not find a matching <img> in <div>.

Warning: Did not expect server HTML to contain a <div> in <div>.
```

Only on that last error did I catch on that this was a problem with server-rendering and the inconsistencies between that and my client render (intentional at the moment while testing some things in unpure render functions).

**What is the expected behavior?**

Being more explicit that this was a rendering inconsistency between server and client.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

React v16-beta.1
}
    if (__DEV__) {
      if (namespaceURI === HTML_NAMESPACE) {
        if (
          !isCustomComponentTag &&
          Object.prototype.toString.call(domElement) ===
            '[object HTMLUnknownElement]' &&
          !Object.prototype.hasOwnProperty.call(warnedUnknownTags, type)
        ) {
          warnedUnknownTags[type] = true;
          warning(
            false,
            'The tag <%s> is unrecognized in this browser. ' +
              'If you meant to render a React component, start its name with ' +
              'an uppercase letter.',
            type,
          );
        }
      }
    }
    return domElement;
  },
  setInitialProperties(
    domElement: Element,
    tag: string,
    rawProps: Object,
    rootContainerElement: Element | Document,
  ): void {
    var isCustomComponentTag = isCustomComponent(tag, rawProps);
    if (__DEV__) {