Presently, Mediawiki provides the system messages:
Such that most user classes can have specific CSS and JS associated with them.
As written, the code explicitly excludes the ability to manage content based on membership in the "user" group of logged-in editors. Is there a good reason for this?
If there is not a specific reason for prohibiting
Then I would suggest that they should be added.
Such a mechanism would provide a natural way to differentiate some content for logged-in editors vs. readers. For example, many message boxes and error messages can be rather cryptic or unhelpful for readers, and it may make sense to provide readers with a more general explanatory statement while showing editors a different and more specific "how do I fix this" kind of message. Obviously any such differentiation would have to be mindful of the fact that IPs can be editors too, but I think decisions about if/when message differentiation is appropriate is more a community issue than a technical one.
So, if there isn't a technical reason that would block this, can we add "user" to the set of classes that can have class-wide CSS and JS pages?