Currently most of the existing classes and id's used in the interface
can conflict with user-specified classes and id's. Unless there are
objections, I will be changing over all of them to begin with a
reserved prefix "mw-", as is the current practice for adding new ones,
and add a check to stop content id's (particularly for headers) from
beginning with "mw-". I may also consolidate some id's that are
different in different skins and change some that are otherwise
inconsistent or weird.
When I finalize the changes, I'll post a full list of them here and on
enwiki VP:T a few days to a week before committing them, so that
people have a chance to update their scripts and CSS. Okay?