One special case of split you haven't mentioned yet is split in void (or scalar) context, which puts the result into @_.

Also, split with the empty pattern splits into separate characters.

As for 'afterthought features' in modern regular expressions, since 5.10 we also have (*...) as 'new syntax'. Before 5.10, (* could not be valid (unless escaped). (+ is up for grabs for the next wave of new features. ;-)