Welcome to WordPress 3.9
A smoother media editing experience
Improved visual editing
The updated visual editor has improved speed, accessibility, and mobile support. You can paste into the visual editor from your word processor without wasting time to clean up messy styling. (Yeah, we’re talking about you, Microsoft Word.)
Edit images easily
With quicker access to crop and rotation tools, it’s now much easier to edit your images while editing posts. You can also scale images directly in the editor to find just the right fit.
Drag and drop your images
Uploading your images is easier than ever. Just grab them from your desktop and drop them onto the editor.
Galleries display a beautiful grid of images right in the editor, just like they do in your published post.
Do more with audio and video
Images have galleries; now we’ve added simple audio and video playlists, so you can showcase your music and clips.
Live widget and header previews
Add, edit, and rearrange your site’s widgets right in the theme customizer. No “save and surprise” — preview your changes live and only save them when you’re ready.
The improved header image tool also lets you upload, crop, and manage headers while customizing your theme.
Stunning new theme browser
Looking for a new theme should be easy and fun. Lose yourself in the boundless supply of free WordPress.org themes with the beautiful new theme browser.
Under the Hood
Semantic Captions and Galleries
Theme developers have new options for images and galleries that use intelligent HTML5 markup.
Inline Code Documentation
Every action and filter hook in WordPress is now documented, along with expanded documentation for the media manager and customizer APIs.
Updated libraries: TinyMCE 4, jQuery 1.11, Backbone 1.1, Underscore 1.6, Plupload 2, MediaElement 2.14, Masonry 3.
Improved Database Layer
Database connections are now more fault-resistant and have improved compatibility with PHP 5.5 and MySQL 5.6.
New Utility Functions
Identify a hook in progress with
doing_filter(), and manipulate custom image sizes with
Plugins and themes registering custom image sizes can now register suggested cropping points. For example, prevent heads from being cropped out of photos with a top-center crop.