When a page with a . or %2E in its name is accessed via ?action=raw , a page saying "<h1>Forbidden</h1><p>Invalid file extension found in the path info or query string.</p>" is returned instead.
To avoid hitting this, either:
- use the full index.php URL: https://en.wikipedia.org/w/index.php?title=Washington_University_in_St._Louis&action=raw
- use the API to fetch data in XML or JSON packaging
Note that action=raw is a very old feature and is not recommended for current use since the API was created some years ago.