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

I want to request a feature.

**What is the current behavior?**

We have no API to verify a ReactNode is a React 16 Fragment. Though now we can use `React.isValidElement(instance) && typeof instance.type === 'symbol'` to distinguish it. It's verbose and seems uncertianly right.

**What is the expected behavior?**

Add api:

```
React.isFragment(object)
```
Verifies the object is a React.Fragment. Returns true or false.

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

React 16.2
]),
      }),
  },
  
  {
    label: 'react-reconciler',
    bundleTypes: [NODE_DEV, NODE_PROD],
    moduleType: RECONCILER,
    entry: 'react-reconciler',
    global: 'ReactReconciler',
    externals: ['react'],
  },
  
  {
    label: 'react-reconciler-persistent',
    bundleTypes: [NODE_DEV, NODE_PROD],
    moduleType: RECONCILER,
    entry: 'react-reconciler/persistent',
    global: 'ReactPersistentReconciler',
    externals: ['react'],
  },
  
  {
    label: 'reconciler-reflection',
    moduleType: RENDERER_UTILS,
    bundleTypes: [NODE_DEV, NODE_PROD],
    entry: 'react-reconciler/reflection',
    global: 'ReactFiberTreeReflection',
    externals: [],
  },