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Changes between Initial Version and Version 1 of Ticket #27320, comment 20

initial	v1
3	3	Unifying media controls and supporting playlists in the editor:
4	4	* Support a caption attribute for audio and video shortcodes
5		* In `wp.media.audio\|video`, rename ~~update to shortcode~~ to allow these models to share the same mixins as `wp.media.collection` subclasses
	5	* In `wp.media.audio\|video`, rename `update` to `shortcode` to allow these models to share the same mixins as `wp.media.collection` subclasses
6	6	* When sending an audio or video shortcode to the editor, create a default caption if the user hasn't entered one. This currently only displays in the editor, not on the front end. Captions aren't tied to a specific attachment here because external sources are supported.
7	7	* In the `wp.mce.media mixin`, in the edit method, read `attr` instead of `data` when attempting to parse the encoded shortcode. data does not automatically update when the attribute changes. This was a blessing to debug.