-`headerLayoutPreset: 'center' | 'left'` to provide an easy solution for [questions like this](https://github.com/react-navigation/react-navigation/issues/4615).
-`headerBackTitleEnabled` - this configuration option for stack navigator allows you to force back button titles to either be rendered or not (if you disagree with defaults for your platform and layout preset).
### Fixed
- Android back button ripple is now appropriately sized (fixes [#3955](https://github.com/react-navigation/react-navigation/issues/3955)).
- Respect header background color on container (fixes edge case where user depended on displaying content that was rendered behind the navigator, this particular behavior should not be depended on and may break in the future, but this change is still useful regardless).
-`headerLeftContainerStyle`, `headerTitleContainerStyle`, and `headerRightContainerStyle` are exposed on `navigationOptions`. These properties allow you to customize the style of the container of `headerLeft`, `headerTitle` and `headerRight` components.
### Fixed
- Fixed memory leaks in `createNavigator`: [closure scope leak](https://github.com/react-navigation/react-navigation/commit/1a765562905e93bbae0262dd20c2688221c999e8), and [clean up old descriptors](https://github.com/react-navigation/react-navigation/commit/93642e16e7ff029586b68ee732ec790504ee4862).
- The enableURLHandling prop on the top level navigator component allows you to disable deep linking handling. Currently it is always enabled. To disable it, `<RootNavigator enableURLHandling={false} />`
- Improve empty path and param handling in deep linking (#4671). This fixes issues with deep linking and fully tests the differences between path: '' and path: null. Empty string matches empty paths, and null path will let the child router handle paths at the same level. Also it makes sure that params are not duplicated between path and query when they are serialized with getPathAndParamsForState.
- Fix onTransitionStart not being invoked when provided in navigator config.(#4100)
- Rare case when users navigated back and forth quickly with exactly the right timing would cause a crash due to a scene being queued to transition, then clobbered, then attempted to render as a stale scene but without a descriptor. ([commit](https://github.com/react-navigation/react-navigation/commit/cab4d71a5e09188df3f4a294c98779eecb860a78))
- [NavigationEvents](https://github.com/react-navigation/react-navigation/pull/4188) component as a declarative interface for subscribing to navigation focus events.
- Avoid crash when calling isFocused on old route (https://github.com/react-navigation/react-navigation/commit/0921889f7a3acfc6d6bcc4909d209eeeee985ba7)
- Stack router no longer attempts to parse query params within path handling
- Switch router now has exact same param treatment for URLs as stack router does
### Changed
- Internally we no longer need to special case PlatformHelpers by platform as react-native-web handles the APIs we mocked out with it now.
- Throw error in development mode when header navigation option is set to a string - a common mistake that would otherwise result in a cryptic error message.
-`setParams` applies to the navigation object it is called on even if that is the navigation object for a navigation view (more details in https://github.com/react-navigation/react-navigation/issues/4497)
