**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
getChildNamespace(parentNamespace: string | null, type: string): string {
    if (parentNamespace == null || parentNamespace === HTML_NAMESPACE) {
      
      return getIntrinsicNamespace(type);
    }
    if (parentNamespace === SVG_NAMESPACE && type === 'foreignObject') {
      
      return HTML_NAMESPACE;
    }
    
    return parentNamespace;
  },
  createElement(
    type: *,
    props: Object,
    rootContainerElement: Element | Document,
    parentNamespace: string,
  ): Element {
    
    
    var ownerDocument: Document = rootContainerElement.nodeType ===
      DOCUMENT_NODE
      ? (rootContainerElement: any)
      : rootContainerElement.ownerDocument;
    var domElement: Element;
    var namespaceURI = parentNamespace;
    if (namespaceURI === HTML_NAMESPACE) {
      namespaceURI = getIntrinsicNamespace(type);
    }
    if (__DEV__) {