[csswg-drafts] [css-text] Clarify how letter-spacing and word-spacing should affect tab-size.

wisniewskit has just created a new issue for 
https://github.com/w3c/csswg-drafts:

== [css-text] Clarify how letter-spacing and word-spacing should 
affect tab-size. ==
Recently it was 
[resolved](https://lists.w3.org/Archives/Public/www-style/2016Oct/0068.html)
 that letter-spacing and word-spacing should affect tab-size, as per 
this 
[proposal](https://lists.w3.org/Archives/Public/www-style/2015Jan/0548.html):

>tab stops are calculated as
>   n*( width of U+0020 plus letter-spacing plus word-spacing)

But this seems strange to me, as tab characters are already affected 
by letter-spacing, aren't they? (That's what I'm seeing while playing 
around in devtools in Firefox and Chrome). Why count letter-spacing 
twice for tabs?

In addition, tabs [aren't word-separators in the 
spec](https://drafts.csswg.org/css-text-3/#word-spacing-property), 
which also states:

>If there are no word-separator characters, or if a word-separating 
character has a zero advance width (such as the zero width space 
U+200B) then the user agent must not create an additional spacing 
between words.

How is this meant to be reconciled? Should the word-spacing be applied
 regardless of whether there are word-separator characters in the run?

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/643 using your GitHub 
account