[whatwg] <time>

[Kristof Zelechovski]

Notation for negative quantities usually starts with a minus (with
exceptions for bookkeeping).  It still does even though ASCII unified the
hyphen with the minus.
We cannot perform interval arithmetic on intervals with unknown limits or
compare them.  Automated processing tools would not benefit from the ability
to recognize such intervals in markup even though they often occur in
ancient biographies.
For the record,
Chris