Media: Remove `alt` fallbacks to improve accessibility.

This removes the fallbacks in `wp_get_attachment_image()` and in
`wp.media.string.props` which attempt to generate an `alt` value
from the image caption or title if an `alt` attribute isn't explicitly
set.

This allows for image HTML to be generated that contains an empty `alt`
value, i.e., `alt=""` which is much preferable for screen readers than
reading redundant content in the case of a caption, or when reading the
image title, which is often generated from the filename and not helpful
as `alt` text.

Props odie2, joedolson, rianrietveld, afercia, iamjolly, joemcgill.
Fixes #34635.
Built from https://develop.svn.wordpress.org/trunk@38812


git-svn-id: http://core.svn.wordpress.org/trunk@38755 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/media-editor.js

@@ -48,28 +48,9 @@
 		 * @returns {Object} Joined props
 		 */
 		props: function( props, attachment ) {
-			var link, linkUrl, size, sizes, fallbacks,
+			var link, linkUrl, size, sizes,
 				defaultProps = wp.media.view.settings.defaultProps;
 
-			// Final fallbacks run after all processing has been completed.
-			fallbacks = function( props ) {
-				// Generate alt fallbacks and strip tags.
-				if ( 'image' === props.type && ! props.alt ) {
-					if ( props.caption ) {
-						props.alt = props.caption;
-					} else if ( props.title !== props.url ) {
-						props.alt = props.title;
-					} else {
-						props.alt = '';
-					}
-
-					props.alt = props.alt.replace( /<\/?[^>]+>/g, '' );
-					props.alt = props.alt.replace( /[\r\n]+/g, ' ' );
-				}
-
-				return props;
-			};
-
 			props = props ? _.clone( props ) : {};
 
 			if ( attachment && attachment.type ) {
@@ -87,7 +68,7 @@
 
 			// All attachment-specific settings follow.
 			if ( ! attachment ) {
-				return fallbacks( props );
+				return props;
 			}
 
 			props.title = props.title || attachment.title;
@@ -123,7 +104,7 @@
 				props.rel = props.rel || 'attachment wp-att-' + attachment.id;
 			}
 
-			return fallbacks( props );
+			return props;
 		},
 		/**
 		 * Create link markup that is suitable for passing to the editor

wp-includes/media.php

@@ -866,12 +866,8 @@ function wp_get_attachment_image($attachment_id, $size = 'thumbnail', $icon = fa
 		$default_attr = array(
 			'src'	=> $src,
 			'class'	=> "attachment-$size_class size-$size_class",
-			'alt'	=> trim(strip_tags( get_post_meta($attachment_id, '_wp_attachment_image_alt', true) )), // Use Alt field first
+			'alt'	=> trim( strip_tags( get_post_meta( $attachment_id, '_wp_attachment_image_alt', true ) ) ),
 		);
-		if ( empty($default_attr['alt']) )
-			$default_attr['alt'] = trim(strip_tags( $attachment->post_excerpt )); // If not, Use the Caption
-		if ( empty($default_attr['alt']) )
-			$default_attr['alt'] = trim(strip_tags( $attachment->post_title )); // Finally, use the title
 
 		$attr = wp_parse_args( $attr, $default_attr );
 

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-alpha-38811';
+$wp_version = '4.7-alpha-38812';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.