Previously slashdash was allowed anywhere `ws` was, and could be
followed by any legal slashdashable token regardless of position. This
caused some ambiguous parsing and enabled constructions we really don't
want.
The new version simply allows a slashdash to preceed each commentable
token, thus restricting its use to locations where the token is
otherwise valid.
The Unicode standard listed VT in its table in §5.8 but that was just a
table of acronyms, and VT was only listed because Microsoft Word used it
as a line separator. VT is not part of its recommendation for characters
to treat as line terminators.