In order to solve Users are not able to browse rar files using Return (although it works for 7z, zip files, etc.), the Internet Media Type "application/vnd.rar" is recognized in KrArcBaseManager::getShortTypeFromMime(const QString &mime).
In https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Complete_list_of_MIME_types the type of rar files is "application/x-rar-compressed", but in the aforementioned page it's also declared that
IANA is the official registry of MIME media types and maintains a [list of all the official MIME types](http://www.iana.org/assignments/media-types/media-types.xhtml)
and precisely in that place what it's stated is "application/vnd.rar", with a link to
where it's written
- Deprecated alias names for this type: application/x-rar-compressed
Note: "application/vnd.rar" is already used in Krusader, in KrServices::generateKrarcArchiveMimetypes().
The text "application/x-rar;application/x-rar-compressed;application/vnd.rar" can be searched in https://github.com/lxde/libfm/blob/master/data/archivers.list
In Kubuntu 18.04 I executed:
$ xdg-mime query default application/x-rar org.kde.ark.desktop $ xdg-mime query default application/x-rar-compressed org.kde.ark.desktop $ xdg-mime query default application/vnd.rar org.kde.ark.desktop $ xdg-mime query default application/vnd.JUST_TO_CHECK_THAT_IT_CAN_FAIL; echo $? 4
Several people had a similar problem when using other programs (https://bbs.archlinux.org/viewtopic.php?pid=1748314#p1748314 , https://github.com/webmin/webmin/issues/702#issue-276713752).