2.2.2.1.13 FileExtensions Element
The <FileExtensions> element SHOULD contain <FileExtension> elements (section 2.2.2.1.14) for all the file types that can be opened by the remote resource defined in section 2.2.2.1.4.<6>
The <FileExtensions> element MUST be set as empty by the server if the remote resource does not handle any file types.