[XeTeX] Font protrusion --- new or old ?

[Will Robertson]

On 2009-02-09 01:06:16 +1030, Jonathan Kew 
<jonathan at jfkew.plus.com> said:

> Basically, borrow the ideas from Appendix D but use the transition
> between class 255 (non-character) and whatever classes you assign to
> the punctuation chars to insert the kerns.

Well! That's quite amazing.
I never even knew that class 255 was encountered at line start and end. 
(Well, actually I never knew where it was found at all!)

Will class 255 turn up in places where hanging punctuation won't be 
appropriate? I'd like to improve the documentation on this detail in 
xetexref, which you might have noticed is pretty anaemic at the 
moment...

W