Accessibility: Ensure embed iframes have a title attribute.

Screen reader users rely on the iframe title attribute to describe the contents of iframes. A meaningful title attribute allows to quickly identify the iframe content, so users can determine which iframe to enter and explore in detail or skip if desired.
Note: this is the only case where a title attribute is required for compliance with the W3C Web Content Accessibility Guidelines (WCAG).

- checks for oEmbed response of type `video` or `rich`
- checks if they use an iframe
- fetches the title (if any) from the oEmbed response
- adds the title to the embed iframe

Props bamadesigner, TomHarrigan, swissspidy, jrf, afercia.
Fixes #40245.

Built from https://develop.svn.wordpress.org/trunk@44942


git-svn-id: http://core.svn.wordpress.org/trunk@44773 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/default-filters.php

@@ -573,6 +573,7 @@ add_filter( 'the_excerpt_embed', 'shortcode_unautop' );
 add_filter( 'the_excerpt_embed', 'wp_embed_excerpt_attachment' );
 
 add_filter( 'oembed_dataparse', 'wp_filter_oembed_result', 10, 3 );
+add_filter( 'oembed_dataparse', 'wp_filter_oembed_iframe_title_attribute', 20, 3 );
 add_filter( 'oembed_response_data', 'get_oembed_response_data_rich', 10, 4 );
 add_filter( 'pre_oembed_result', 'wp_filter_pre_oembed_result', 10, 3 );
 

wp-includes/embed.php

@@ -780,6 +780,55 @@ function _oembed_create_xml( $data, $node = null ) {
 	return $node->asXML();
 }
 
+/**
+ * Filters the given oEmbed HTML to make sure iframes have a title attribute.
+ *
+ * @since 5.2.0
+ *
+ * @param string $result The oEmbed HTML result.
+ * @param object $data   A data object result from an oEmbed provider.
+ * @param string $url    The URL of the content to be embedded.
+ * @return string The filtered oEmbed result.
+ */
+function wp_filter_oembed_iframe_title_attribute( $result, $data, $url ) {
+	if ( false === $result || ! in_array( $data->type, array( 'rich', 'video' ) ) ) {
+		return $result;
+	}
+
+	$title = ! empty( $data->title ) ? $data->title : '';
+
+	$pattern        = '`<iframe[^>]*?title=(\\\\\'|\\\\"|[\'"])([^>]*?)\1`i';
+	$has_title_attr = preg_match( $pattern, $result, $matches );
+
+	if ( $has_title_attr && ! empty( $matches[2] ) ) {
+		$title = $matches[2];
+	}
+
+	/**
+	 * Filters the title attribute of the given oEmbed HTML iframe.
+	 *
+	 * @since 5.2.0
+	 *
+	 * @param string $title  The title attribute.
+	 * @param string $result The oEmbed HTML result.
+	 * @param object $data   A data object result from an oEmbed provider.
+	 * @param string $url    The URL of the content to be embedded.
+	 */
+	$title = apply_filters( 'oembed_iframe_title_attribute', $title, $result, $data, $url );
+
+	if ( '' === $title ) {
+		return $result;
+	}
+
+	if ( $has_title_attr ) {
+		// Remove the old title, $matches[1]: quote, $matches[2]: title attribute value.
+		$result = str_replace( ' title=' . $matches[1] . $matches[2] . $matches[1], '', $result );
+	}
+
+	return str_ireplace( '<iframe ', sprintf( '<iframe title="%s" ', esc_attr( $title ) ), $result );
+}
+
+
 /**
  * Filters the given oEmbed HTML.
  *

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.2-alpha-44941';
+$wp_version = '5.2-alpha-44942';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.