This is all API and Backend changes in WordPress 4.2 for you developers only. Some interesting changes make WordPress backend more awesome than before.

• • The new wp.a11y.speak() API is available. When a change on the page happens, you can make sure that screen reader users are notified with this helper.
  • The default admin color scheme has been tweaked. Minor, but if you use the WordPress colors directly in your code, you should update the code.
  • When possible, WordPress now will use utf8mb4 as the database character set.
  • Terms shared across multiple taxonomies will now be split into separate terms when one of them is updated.
  • The experimental TinyMCE views API has continued to evolve. As this is an experimental API, use in production is not recommended unless you closely follow the development as breaking changes are possible.
  • Two UI components used by core, spinners and admin notices, have been improved. The change to spinners is a change to how they are added and the change to admin notices is the ability to optionally make them dismissible.
  • Complex queries - Support specific meta_query clauses to be used withorderby, added to WP_Query, WP_Comment_Query, andWP_User_Query