## Serialization of control characters with DataContractJsonSerializer is now compatible with ECMAScript V6 and V8

### Scope
Edge

### Version Introduced
4.7

### Source Analyzer Status
Planned

### Change Description

In the .NET framework 4.6.2 and earlier versions, the
<xref:System.Runtime.Serialization.Json.DataContractJsonSerializer?displayProperty=name>
did not serialize some special control characters, such as \b, \f, and \t, in a
way that was compatible with the ECMAScript V6 and V8 standards. Starting with
the .NET Framework 4.7, serialization of these control characters is compatible
with ECMAScript V6 and V8.

- [x] Quirked
- [ ] Build-time break

### Recommended Action

For apps that target the .NET Framework 4.7, this feature is enabled by default.
If this behavior is not desirable, you can opt out of this feature by adding the
following line to the `<runtime>` section of the app.config or web.config file:

   ```xml
   <runtime>
      <AppContextSwitchOverrides value="Switch.System.Runtime.Serialization.DoNotUseECMAScriptV6EscapeControlCharacter=false" />
   </runtime>
   ```

### Affected APIs
* `M:System.Runtime.Serialization.Json.DataContractJsonSerializer.WriteObject(System.IO.Stream,System.Object)`
* `M:System.Runtime.Serialization.Json.DataContractJsonSerializer.WriteObject(System.Xml.XmlDictionaryWriter,System.Object)`
* `M:System.Runtime.Serialization.Json.DataContractJsonSerializer.WriteObject(System.Xml.XmlWriter,System.Object)`

### Category
Windows Communication Foundation (WCF)

<!-- breaking change id: 168 -->