Document visual diff review for the web editor

editor/publish.mdx

@@ -49,6 +49,17 @@ When you work on a feature branch, save changes to the branch.
 
 To discard changes, click **Undo changes** beside a filename in the files changed dropdown.
 
+### Review changes
+
+Click a filename in the files changed dropdown to see what changed. The editor opens a diff view that highlights additions, deletions, and modifications so you can review your edits before publishing.
+
+The diff view mode depends on your current editing mode:
+
+- **Visual diff**: When you are in visual mode, the editor shows a rendered preview with colored markers in the gutter. Green markers indicate additions, red markers indicate deletions, and blue markers indicate modifications.
+- **Markdown diff**: When you are in Markdown mode, the editor shows a side-by-side comparison of the raw source.
+
+Use the mode toggle in the toolbar to switch between visual and Markdown diff views. Click the <Icon icon="xmark" /> button next to the mode toggle to exit the diff view and return to editing.
+
 ### Publish your changes
 
 Click **Publish** in the toolbar. Depending on your workflow, your changes deploy immediately or create a pull request for you to merge in your Git provider. If you are on a feature branch, save your changes before publishing.