Game Boy, problem with Jscript is people turn it off or sometimes don't even have access to it... and XML is going to work on even less systems, so for a chat system, it might work well, if it degrades nicely into what I described before, but it couldn't possibly work for a game and degrade well...
I'm sure there is another way, some kind of old old old school vintage 1994 chat tech.
I'm sure there is another way, some kind of old old old school vintage 1994 chat tech.