Merge pull request #2373 from genbit/docs-animation-props

Update 09.1-animation.md

docs/docs/09.1-animation.md

@@ -175,3 +175,11 @@ By default `ReactTransitionGroup` renders as a `span`. You can change this behav
 ```
 
 Every DOM component is under `React.DOM`. However, `component` does not need to be a DOM component. It can be any React component you want; even ones you've written yourself!
+
+Any additional, user-defined, properties will be become properties of the rendered component. For example, here's how you would you render a `<ul>` with css class:
+
+```javascript{1}
+<ReactTransitionGroup component={React.DOM.ul} className="animated-list">
+  ...
+</ReactTransitionGroup>
+```