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Re: [css3-text-layout] margin-before/after/start/end etc. and :ttb pseudo-classes

From: Håkon Wium Lie <howcome@opera.com>
Date: Sat, 5 Jun 2010 21:51:52 +0200
Message-ID: <19466.43736.906577.114035@gargle.gargle.HOWL>
To: Andrew Thompson <lordpixel@mac.com>
Cc: www style <www-style@w3.org>
Also sprach Andrew Thompson:

 > The objection is :ltr/:rtl/:ttb would depend on the value of
 > writing-direction determined for a given element in the document
 > and similar proposals have been rejected before for good reasons.

Yes.

 > Murata-san – I think – might be satisfied if there was a way to say
 > 'when the user's preference is set to vertical text, the following
 > rules apply'.
 > 
 > So is it reasonable to separate :ltr and :rtl to be a shorthand for
 > inherited [dir] but to explicitly define :ttb as something entirely
 > different?

I think so. I previously suggested:

  :lrt   horizontal writing is supported and @dir has been set to 'lrt'
  :rtl   horizontal writing is supported and @dir has been set to 'rtl'
  :ttb   vertial writing is supported

 > A selector whose matching solely depends on whether the
 > user prefers this (part of?) the document to be vertical?
 > Quoting CSS 2 5.10: "CSS introduces the concepts of pseudo-elements
 > and pseudo-classes to permit formatting based on information that
 > lies outside the document tree."

Good reading of the spec. I believe this falls within the scope of
pseudo-classes.

One option would be to tie this directly to a user preference. This
would force UAs to offer a UI for setting the preferred writing mode.
This would be a novel requirement; in the past, such UI preferences
have been commmunicated to the CSS formatter by way of properties and
values. However, if we accept that change, we could say:

  :lrt   horizontal writing is supported and @dir has been set to 'lrt'
  :rtl   horizontal writing is supported and @dir has been set to 'rtl'
  :ttb   vertial writing is supported and the user has indicated that
         vertical writing is preferred.

A variation of this would be to tie :ttb to the initial value of the
'writing-mode' property. We would then say:

  :lrt   horizontal writing is supported and @dir has been set to 'lrt'
  :rtl   horizontal writing is supported and @dir has been set to 'rtl'
  :ttb   vertial writing is supported and the initial value of
         'writing-mode' is 'tb-rl'

The initial value of 'writing-mode' could then be a way for the UA to
communicate the preferred writing-mode to the CSS formatter. UAs could
offer a UI so that users would influence the initial value of
'writing-mode' and thereby the writing direction.

(The shorthand 'writing-mode' doesn't have an initial value, but the
individual 'block-flow' has. Therefore, it would probably be the
initial value of 'block-flow' that should be used -- even if it feels
less intuitive.)

 > Or for that matter, someone proposed a media query... certainly one
 > could argue a user preference for vertical layout is reasonably
 > within that definition.

That would be a longer stretch, but not impossibly so. Code like this
could work:

@media (block-direction: rl) { ... }
@media (preferred-writing-mode: vertical) { ... }
@media (ttb) { ... }

Cheers,

-h&kon
              Håkon Wium Lie                          CTO °þe®ª
howcome@opera.com                  http://people.opera.com/howcome
Received on Saturday, 5 June 2010 20:36:29 GMT

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