Previously I wrote a temporary solution to the issue using CSS sibling selectors (b.pn + b.pn) [1], which would give the two elements a small space in between. In my opinion, none of the solution and inserting " " or " " is semantically correct.
In Chinese writing rules, we cannot find the use of half-width space of these kinds. Also, the tiny small separation of the punctuation (proper nouns and citation marks) can only be seen in the "decorative lines". The character-spacing is supposed to remain the same as non-formatted one. Therefore, I strongly suggest that we have "special provisions of underlines".
(Chinese) http://lists.w3.org/Archives/Public/public-html-ig-zh/2010Sep/0091.html
¦b Dec 4, 2010 3:56 AM ®É¡A Ambrose LI ¼g¨ì¡G
> 2010/12/3 John Cowan <cowan@mercury.ccil.org>
>>
>> KangHao Lu (Kenny) scripsit:
>>
>>> The purpose is for the reader to visually tell
>>>
>>> <p><u>A</u><u>B</u></p>
>>>
>>> and
>>>
>>> <p><u>AB</u></p>
>>>
>>> apart by leaving a very tiny space at the beginning and end of a text
>>> decoration.
>>
>> This can be handled by inserting   or  , at least in non-gridded text.
>
> If we go for spaces we might as well just write a CSS rule for u+u,
> which I think is cleaner. It would also be more consistent, in the
> sense that if we are going to use spaces between proper nouns we might
> as well mark all word boundaries with spaces, but that's not the usual
> way we write Chinese. (Personally I'm very disappointed that u got
> deprecated as "visual formatting", since for us it is semantic markup.
> But that'd be OT.)
>
> --
> cheers,
> -ambrose