When operating via callbacks, the ASPxSpellChecker control can send compressed callback data to compression-enabled browsers, improving the application performance and reducing the traffic. Enabling compression is one of the fastest ways to improve your site's performance.
To exchange the compressed data, both server and a client must agree to do so. The browser sends a header indicating that it accepts compressed content (gzip and deflate are two compression schemes): Accept-Encoding: gzip, deflate. The ASPxSpellChecker checks if encoding is allowed by the browser, and sends a response with the compressed content: Content-Encoding: gzip