Web Audio API
With Safari support for CSS filters, you can use CSS to create advanced filter and pixel effects such as blurs and gradients. CSS filters also let you vary brightness, adjust hues, invert colors or convert elements to sepia or grayscale. You can animate changes to a filter or combine multiple filters, all while tapping into hardware acceleration for fast, smooth rendering.
HTML5 web notifications
Keep your users up-to-date. When a user has your website open, your notifications appear in the new Notification Center in Mountain Lion. Extensions enabled in Safari can also send notifications.
HTML5 timed text tracks
HTML5 timed text tracks make it easy to specify the timing of any text that appears with a media element, such as captions, subtitles, descriptions, and chapters.
HTML5 media synchronization
With support for HTML5 media synchronization, Safari makes it easy to develop webpages that require precise timing integration between multiple media elements.
Private Browsing detection
Extensions can now detect when Private Browsing is on, creating new feature opportunities for extensions that focus on web privacy. Developers of all kinds of extensions can use this feature to fall back gracefully when their extension attempts to access features that aren’t available in Private Browsing mode, such as cookie or data storage.
You can now build extensions that use stylesheets and scripts to change the appearance of articles viewed in Safari Reader.
Redesigned Web Inspector
The Web Inspector has a streamlined new design that speeds up common development tasks.
Navigators appear on the left side of the Web Inspector. Navigators show resources for your page, cookies and storage used, instruments for performance measurement, a central search interface, issue tracking, the debugging stack trace, active and inactive breakpoints, and a collection logs for each reload. Hot keys make switching between navigators fast.
The Jump Bar at the top of the Web Inspector shows the location of your current view. Click any location in the bar to jump to any other element at that level.
Select Show Page Source in the Develop menu to open the new Web Inspector and go straight to the source code. Enjoy the full benefits of syntax highlighting and link-based navigation to referenced sub resources.