There is defined MIME type x-epoc/x-sisx-app. In the whole freedesktop.org.xml it is the only MIME type using x- in the first part of MIME type, and the newly introduced x-epoc/ MIME category contains just this one MIME type. That is why I guess that this definition is a mistake and should be something like application/x-epoc-sisx-app or application/vnd.epoc.sisx-app
x-epoc/x-sisx-app is the mime-type recommended upstream for .sis Symbian application installers.
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.