If multiple children have the same key, for example ([jsfiddle](https://jsfiddle.net/olegs/p09cweky/1/)):

``` javascript
var Hello = React.createClass({
    render: function() {
        return (<ul>
        <li key={"1"}>what</li>
        <li key={"1"}>what</li>
        </ul>
        )
    }
});
```

React prints the following warning to the console:

```
Warning: flattenChildren(...): Encountered two children with the same key, `.$1`. Child keys must be unique; when two children share a key, only the first child will be used.
```

The key referenced in the warning prepends an internal-looking '.$' to the key specified by the user. This is a bit misleading - ideally, it would mention the exact key value set by the user.

return userProvidedKeyEscaperLookup[match];
}
/**
 * Generate a key string that identifies a component within a set.
 *
 * @param {*} component A component that could contain a manual key.
 * @param {number} index Index that is used if a manual key is not provided.
 * @return {string}
 */
function getComponentKey(component, index) {
  
  
  if (component && typeof component === 'object' && component.key != null) {
    
    return wrapUserProvidedKey(component.key);
  }
  
  return index.toString(36);
}
/**
 * Escape a component key so that it is safe to use in a reactid.
 *
 * @param {*} text Component key to be escaped.
 * @return {string} An escaped string.
 */
function escapeUserProvidedKey(text) {