am string $content
 * @return string
 */
function prepend_attachment($content) {
	$post = get_post();

	if ( empty($post->post_type) || $post->post_type != 'attachment' )
		return $content;

	if ( wp_attachment_is( 'video', $post ) ) {
		$meta = wp_get_attachment_metadata( get_the_ID() );
		$atts = array( 'src' => wp_get_attachment_url() );
		if ( ! empty( $meta['width'] ) && ! empty( $meta['height'] ) ) {
			$atts['width'] = (int) $meta['width'];
			$atts['height'] = (int) $meta['height'];
		}
		if ( has_post_thumbnail() ) {
			$atts['poster'] = wp_get_attachment_url( get_post_thumbnail_id() );
		}
		$p = wp_video_shortcode( $atts );
	} elseif ( wp_attachment_is( 'audio', $post ) ) {
		$p = wp_audio_shortcode( array( 'src' => wp_get_attachment_url() ) );
	} else {
		$p = '<p class="attachment">';
		// show the medium sized image representation of the attachment if available, and link to the raw file
		$p .= wp_get_attachment_link(0, 'medium', false);
		$p .= '</p>';
	}

	/**
	 * Filters the attachment markup to be prepended to the post content.
	 *
	 * @since 2.0.0
	 *
	 * @see prepend_attachment()
	 *
	 * @param string $p The attachment HTML output.
	 */
	$p = apply_filters( 'prepend_attachment', $p );

	return "$p\n$content";
}

//
// Misc
//

/**
 * Retrieve protected post password form content.
 *
 * @since 1.0.0
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global $post.
 * @return string HTML content for password form for password protected post.
 */
function get_the_password_form( $post = 0 ) {
	$post = get_post( $post );
	$label = 'pwbox-' . ( empty($post->ID) ? rand() : $post->ID );
	$output = '<form action="' . esc_url( site_url( 'wp-login.php?action=postpass', 'login_post' ) ) . '" class="post-password-form" method="post">
	<p>' . __( 'This content is password protected. To view it please enter your password below:' ) . '</p>
	<p><label for="' . $label . '">' . __( 'Password:' ) . ' <input name="post_password" id="' . $label . '" type="password" size="20" /></label> <input type="submit" name="Submit" value="' . esc_attr_x( 'Enter', 'post password form' ) . '" /></p></form>
	';

	/**
	 * Filters the HTML output for the protected post password form.
	 *
	 * If modifying the password field, please note that the core database schema
	 * limits the password field to 20 characters regardless of the value of the
	 * size attribute in the form input.
	 *
	 * @since 2.7.0
	 *
	 * @param string $output The password form HTML output.
	 */
	return apply_filters( 'the_password_form', $output );
}

/**
 * Whether currently in a page template.
 *
 * This template tag allows you to determine if you are in a page template.
 * You can optionally provide a template name or array of template names
 * and then the check will be specific to that template.
 *
 * @since 2.5.0
 * @since 4.2.0 The `$template` parameter was changed to also accept an array of page templates.
 * @since 4.7.0 Now works with any post type, not just pages.
 *
 * @param string|array $template The specific template name or array of templates to match.
 * @return bool True on success, false on failure.
 */
function is_page_template( $template = '' ) {
	if ( ! is_singular() ) {
		return false;
	}

	$page_template = get_page_template_slug( get_queried_object_id() );

	if ( empty( $template ) )
		return (bool) $page_template;

	if ( $template == $page_template )
		return true;

	if ( is_array( $template ) ) {
		if ( ( in_array( 'default', $template, true ) && ! $page_template )
			|| in_array( $page_template, $template, true )
		) {
			return true;
		}
	}

	return ( 'default' === $template && ! $page_template );
}

/**
 * Get the specific template name for a given post.
 *
 * @since 3.4.0
 * @since 4.7.0 Now works with any post type, not just pages.
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global $post.
 * @return string|false Page template filename. Returns an empty string when the default page template
 * 	is in use. Returns false if the post does not exist.
 */
function get_page_template_slug( $post = null ) {
	$post = get_post( $post );

	if ( ! $post ) {
		return false;
	}

	$template = get_post_meta( $post->ID, '_wp_page_template', true );

	if ( ! $template || 'default' == $template ) {
		return '';
	}

	return $template;
}

/**
 * Retrieve formatted date timestamp of a revision (linked to that revisions's page).
 *
 * @since 2.6.0
 *
 * @param int|object $revision Revision ID or revision object.
 * @param bool       $link     Optional, default is true. Link to revisions's page?
 * @return string|false i18n formatted datetimestamp or localized 'Current Revision'.
 */
function wp_post_revision_title( $revision, $link = true ) {
	if ( !$revision = get_post( $revision ) )
		return $revision;

	if ( !in_array( $revision->post_type, array( 'post', 'page', 'revision' ) ) )
		return false;

	/* translators: revision date format, see https://secure.php.net/date */
	$datef = _x( 'F j, Y @ H:i:s', 'revision date format' );
	/* translators: %s: revision date */
	$autosavef = __( '%s [Autosave]' );
	/* translators: %s: revision date */
	$currentf  = __( '%s [Current Revision]' );

	$date = date_i18n( $datef, strtotime( $revision->post_modified ) );
	if ( $link && current_user_can( 'edit_post', $revision->ID ) && $link = get_edit_post_link( $revision->ID ) )
		$date = "<a href='$link'>$date</a>";

	if ( !wp_is_post_revision( $revision ) )
		$date = sprintf( $currentf, $date );
	elseif ( wp_is_post_autosave( $revision ) )
		$date = sprintf( $autosavef, $date );

	return $date;
}

/**
 * Retrieve formatted date timestamp of a revision (linked to that revisions's page).
 *
 * @since 3.6.0
 *
 * @param int|object $revision Revision ID or revision object.
 * @param bool       $link     Optional, default is true. Link to revisions's page?
 * @return string|false gravatar, user, i18n formatted datetimestamp or localized 'Current Revision'.
 */
function wp_post_revision_title_expanded( $revision, $link = true ) {
	if ( !$revision = get_post( $revision ) )
		return $revision;

	if ( !in_array( $revision->post_type, array( 'post', 'page', 'revision' ) ) )
		return false;

	$author = get_the_author_meta( 'display_name', $revision->post_author );
	/* translators: revision date format, see https://secure.php.net/date */
	$datef = _x( 'F j, Y @ H:i:s', 'revision date format' );

	$gravatar = get_avatar( $revision->post_author, 24 );

	$date = date_i18n( $datef, strtotime( $revision->post_modified ) );
	if ( $link && current_user_can( 'edit_post', $revision->ID ) && $link = get_edit_post_link( $revision->ID ) )
		$date = "<a href='$link'>$date</a>";

	$revision_date_author = sprintf(
		/* translators: post revision title: 1: author avatar, 2: author name, 3: time ago, 4: date */
		__( '%1$s %2$s, %3$s ago (%4$s)' ),
		$gravatar,
		$author,
		human_time_diff( strtotime( $revision->post_modified ), current_time( 'timestamp' ) ),
		$date
	);

	/* translators: %s: revision date with author avatar */
	$autosavef = __( '%s [Autosave]' );
	/* translators: %s: revision date with author avatar */
	$currentf  = __( '%s [Current Revision]' );

	if ( !wp_is_post_revision( $revision ) )
		$revision_date_author = sprintf( $currentf, $revision_date_author );
	elseif ( wp_is_post_autosave( $revision ) )
		$revision_date_author = sprintf( $autosavef, $revision_date_author );

	/**
	 * Filters the formatted author and date for a revision.
	 *
	 * @since 4.4.0
	 *
	 * @param string  $revision_date_author The formatted string.
	 * @param WP_Post $revision             The revision object.
	 * @param bool    $link                 Whether to link to the revisions page, as passed into
	 *                                      wp_post_revision_title_expanded().
	 */
	return apply_filters( 'wp_post_revision_title_expanded', $revision_date_author, $revision, $link );
}

/**
 * Display list of a post's revisions.
 *
 * Can output either a UL with edit links or a TABLE with diff interface, and
 * restore action links.
 *
 * @since 2.6.0
 *
 * @param int|WP_Post $post_id Optional. Post ID or WP_Post object. Default is global $post.
 * @param string      $type    'all' (default), 'revision' or 'autosave'
 */
function wp_list_post_revisions( $post_id = 0, $type = 'all' ) {
	if ( ! $post = get_post( $post_id ) )
		return;

	// $args array with (parent, format, right, left, type) deprecated since 3.6
	if ( is_array( $type ) ) {
		$type = ! empty( $type['type'] ) ? $type['type']  : $type;
		_deprecated_argument( __FUNCTION__, '3.6.0' );
	}

	if ( ! $revisions = wp_get_post_revisions( $post->ID ) )
		return;

	$rows = '';
	foreach ( $revisions as $revision ) {
		if ( ! current_user_can( 'read_post', $revision->ID ) )
			continue;

		$is_autosave = wp_is_post_autosave( $revision );
		if ( ( 'revision' === $type && $is_autosave ) || ( 'autosave' === $type && ! $is_autosave ) )
			continue;

		$rows .= "\t<li>" . wp_post_revision_title_expanded( $revision ) . "</li>\n";
	}

	echo "<div class='hide-if-js'><p>" . __( 'JavaScript must be enabled to use this feature.' ) . "</p></div>\n";

	echo "<ul class='post-revisions hide-if-no-js'>\n";
	echo $rows;
	echo "</ul>";
}