Merge "Message documentation update for DifferenceEngine"

diff --git a/includes/diff/DifferenceEngine.php b/includes/diff/DifferenceEngine.php
index 4ca8263..f3dc5a3 100644 (file)
--- a/includes/diff/DifferenceEngine.php
+++ b/includes/diff/DifferenceEngine.php
@@ -714,12 +714,19 @@ class DifferenceEngine extends ContextSource {
        /**
         * Generate a diff, no caching.
         *
-        * Subclasses may override this to provide a
+        * This implementation uses generateTextDiffBody() to generate a diff based on the default
+        * serialization of the given Content objects. This will fail if $old or $new are not
+        * instances of TextContent.
+        *
+        * Subclasses may override this to provide a different rendering for the diff,
+        * perhaps taking advantage of the content's native form. This is required for all content
+        * models that are not text based.
         *
         * @param $old Content: old content
         * @param $new Content: new content
         *
         * @since 1.21
+        * @throws MWException if $old or $new are not instances of TextContent.
         */
        function generateContentDiffBody( Content $old, Content $new ) {
                if ( !( $old instanceof TextContent ) ) {