1. New default “Twenty thirteen” theme.
2. Various admin back-end enhancements, like menus UI improvements, revisions revised to be more dynamic and scalable, autosave and post locking, preview audio and video on media edit screen, in-line login following expired sessions.
3. Delicious for developers: external libraries have been updated. More info new audio/video APIs give developers access to powerful media metadata, like ID3 tags. Filters for revisions, allowing you to set the number of revisions ad hoc instead of only via a define. More info semantic markup allows themes to chose improved HTML5 markup for comment forms, search forms, and comment lists. Search content for shortcodes with has_shortcode() and adjust shortcode attributes with a new filter.
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