Re: [css-values][css-writing-modes] ch and ic units

> On Mar 9, 2016, at 16:43, Koji Ishii <kojiishi@gmail.com> wrote:
> 
> On Sun, Mar 6, 2016 at 7:00 PM, Florian Rivoal <florian@rivoal.net <mailto:florian@rivoal.net>> wrote:
> 
> 2) "advance measure", as used in the definition of both the ch and ic units isn't defined, and we need to clarify how it works in vertical writing modes. Since they are typically used to set the inline size of something in terms of a number of characters, it would makes sense to me in
> - in "writing-mode:sideways-*" or "writing-mode:vertical-*;"text-orientation:sideways", advance measure for both units means advance width
> - in text-orientation:upright, advance measure for both units means advance height
> - in text-orientation:mixed, ch should use the advance width, which ic should use the advance height.
> 
> For CJK authors, "ch" is quite useful to get the approximate width of non-CJK characters, and in CJK vertical flow, the height is almost 1em.
> 
> With your proposal, authors will lose a way to get the former, and makes "ch" equivalent to "em" except for very few exceptional fonts.
> 
> I prefer "ch" always be the "width of "0" glyph, or 0.5em" as what authors lose looks more than what authors get.

Why is the width of the 0 character interesting if text is set upright? If it is mixed or sideways, I agree width is the right measure, but for upright I don't see it.

 - Florian