Pages: Mention splats and domain redirects in _redirects post

content/codeberg-pages/advanced-usage.md

@@ -69,4 +69,15 @@ Redirects every path under `/articles` to `/posts` while keeping the path.
 
 {% endadmonition %}
 
+Redirection with splats might have exclamation mark after the redirect code (`302!`) to redirect all paths, not only those that weren't found.
+
 Example: `/articles/2022/10/12/post-1/` → `/posts/2022/10/12/post-1/`
+
+#### Domain redirects
+
+You can use redirects as a way to "canonicalize" one subdomain into another (or into a toplevel domain.)
+For that, use double slash and list the full address, likely with splats:
+
+```text
+//www.example.org/* https://example.org/:splat 302!
+```