Ticket #33979: 33979-2.diff

src/wp-includes/media.php

@@ -1824 +1824 @@
                 if ( isset( $image_meta['height'], $image_meta['width'] ) ) {
                         $orientation = ( $image_meta['height'] > $image_meta['width'] ) ? 'portrait' : 'landscape';
                 }
-                $output .= "<{$itemtag} class='gallery-item'>";
+                /** 
+                * Filter the gallery item classes. 
+                * 
+                * @since 4.9.3 
+                * 
+                * @param string $classes    Classes applied to gallery item. 
+                * @param object $attachment Attachment object. 
+                */ 
+                $classes = 'gallery-item'; 
+                $gallery_item_classes = apply_filters( 'gallery_item_classes', $classes, $attachment ); 
+                $output .= "<{$itemtag} class='{$gallery_item_classes}'>"; 
                 $output .= "
                         <{$icontag} class='gallery-icon {$orientation}'>
                                 $image_output