MSPs process static files in a special way because the relative URL actually refers to the MSP servlet, which reads and returns the appropriate content. The file extensions that the MSP servlet recognizes as valid static content are set by the configuration parameter StaticFileExtensions. The default value is as follows.
If you do not wish to serve any static files from your site, you can omit this definition. Alternatively, you could add extensions for other formats, such as sound or scripting archives.