Document suppressHydrationWarning (#369)

* Document suppressHydrationWarning

* Add it to the reference

content/docs/reference-dom-elements.md

@@ -112,6 +112,12 @@ Not all style properties are converted to pixel strings though. Certain ones rem
 
 Normally, there is a warning when an element with children is also marked as `contentEditable`, because it won't work. This attribute suppresses that warning. Don't use this unless you are building a library like [Draft.js](https://facebook.github.io/draft-js/) that manages `contentEditable` manually.
 
+### suppressHydrationWarning
+
+If you use server-side React rendering, normally there is a warning when the server and the client render different content. However, in some rare cases, it is very hard or impossible to guarantee an exact match. For example, timestamps are expected to differ on the server and on the client.
+
+If you set `suppressHydrationWarning` to `true`, React will not warn you about mismatches in the attributes and the content of that element. It only works one level deep, and is intended to be used as an escape hatch. Don't overuse it. You can read more about hydration in the [`ReactDOM.hydrate()` documentation](/docs/react-dom.html#hydrate).
+
 ### value
 
 The `value` attribute is supported by `<input>` and `<textarea>` components. You can use it to set the value of the component. This is useful for building controlled components. `defaultValue` is the uncontrolled equivalent, which sets the value of the component when it is first mounted.

content/docs/reference-react-dom.md

@@ -64,7 +64,9 @@ ReactDOM.hydrate(element, container[, callback])
 
 Same as [`render()`](#render), but is used to hydrate a container whose HTML contents were rendered by [`ReactDOMServer`](/docs/react-dom-server.html). React will attempt to attach event listeners to the existing markup.
 
-React expects that the rendered content is identical between the server and the client. It can patch up differences in text content (such as timestamps), but you should treat mismatches as bugs and fix them. In development mode, React warns about mismatches during hydration. There are no guarantees that attribute differences will be patched up in case of mismatches. This is important for performance reasons because in most apps, mismatches are rare, and so validating all markup would be prohibitively expensive.
+React expects that the rendered content is identical between the server and the client. It can patch up differences in text content, but you should treat mismatches as bugs and fix them. In development mode, React warns about mismatches during hydration. There are no guarantees that attribute differences will be patched up in case of mismatches. This is important for performance reasons because in most apps, mismatches are rare, and so validating all markup would be prohibitively expensive.
+
+If a single element's attribute or text content is unavoidably different between the server and the client (for example, a timestamp), you may silence the warning by adding `suppressHydrationWarning={true}` to the element. It only works one level deep, and is intended to be an escape hatch. Don't overuse it. Unless it's text content, React still won't attempt to patch it up, so it may remain inconsistent until future updates.
 
 If you intentionally need to render something different on the server and the client, you can do a two-pass rendering. Components that render something different on the client can read a state variable like `this.state.isClient`, which you can set to `true` in `componentDidMount()`. This way the initial render pass will render the same content as the server, avoiding mismatches, but an additional pass will happen synchronously right after hydration. Note that this approach will make your components slower because they have to render twice, so use it with caution.