Per https://bugs.webkit.org/show_bug.cgi?id=101953 we should maybe standardize the message member too instead of leaving it implementation-defined.
That bug is about making the message more informative, right?
This bug is about a wider thing: it would also prevent making the message even more informative without a spec change...
Right. I'm not sure that's desirable, but then I'm not sure it's desirable to expose UA-dependent strings either.
This change would also prevent making the message informative for developers who don't speak English by localizing it.
I think I lean towards not having prescribed messages for DOM exceptions, but either way Web IDL already has a hook for other specs to state what the message is, so I don't think the spec needs changing.
Alright, not worth it.