Create a custom shortcode handler for video playlists.
Use <amp-video> and <amp-state>, on Weston't suggestion.
This still doesn't support audio playlists.

Before, test_shortcode() used test files from Core.
But these did not exist in 4.7, and caused a failure.
So create new mock files to test.

Use an <amp-carousel>,
As <amp-bind> doesn't work with <amp-audio>.
Abstract common logic into helper methods.
This mainly allows using styling from
wp-mediaelement.css.
But there are 4 rules needed to correct the styling.

The video and audio playlist need 'wp-mediaelement.'
And the audio playlist needs a simple custom stylesheet.
Use the action 'wp_enqueue_scripts,'
instead of 'wp_playlist_script.'
That enqueues too late.
Also, update the tests.

At Weston's suggestion.
This is easier to understand.

Before, the output was only escaped
if the value was set.
Also, remove the isset() check for $title.
As Weston mentioned, this is always a string.

Inside a conditional, return an empty string.
As Weston mentioned, the PHP DocBlock
indicates a string return value.
Also, add an assertion for this.
And correct the documentation of 'content_width.'

Props @westonruter for the new regex.
Also, remove periods from '@return void.'

On Weston's suggestion.
This function should return the shortcode
to the state before this embed handler changed it.
So it stores the previous callback in $removed_shortcode.
And it adds that callback in remove_embed().

As Weston mentioned, the DocBlock indicates an array().
So return an empty array instead of void.

This should always be present.
@see wp_playlist_shortcode().

Audio playlists have thumbnail images.
If the height and width aren't defined in $data,
Set fallbacks.
These are based on the fallback heights in:
wp_playlist_shortcode().

The playlist is actually a carousel,
as it's not possible to use <amp-bind>.
But that doesn't match native WP UI.
So remove the buttons that go other carousel items.
One can click the tracks to go to another track.

* Restore wp_print_head_scripts and wp_print_footer_scripts.
* Return associative array instead of positional array in get_thumb_dimensions.
* Further clean phpdoc.

…ut anyway

* Remove script output by wp_comment_form_unfiltered_html_nonce().
* Remove wp-embed script enqueued by wp_oembed_add_host_js().

…dd/841-amp-video-playlist