Re: [css-inline] constant leading and dominant baselines

On Monday 2015-02-09 21:21 +0900, John Daggett wrote:
> One of these is the ability to fix the leading between lines.  Even when a
> fixed line-height value is specified, the actual height of the linebox may
> change due to variations in the fonts or content included in a line or due
> to alignment variations. Common examples in existing web content are the
> use of HTML synthetic superscripts or lines involving multiple fonts with
> different line metrics. The benefit of this variable line height model is
> that the contents of one line never collide with the contents of the lines
> above or below it. The downside is that when line placement varies it often
> does so in ways that are unnecessary and detract from the readability.
> 
> To allow high quality, constant leading, a 'line-height-style' property
> would be very useful:
> 
>   line-height-style: variable | fixed
> 
> The initial value would be 'variable' and would represent current behavior.
> Lines would be placed based at the maximum of the line-height value and the
> height of the current linebox. The 'fixed' value would specify that lines
> would always be placed a constant distance apart, independent of the height
> of the linebox.
> 
> Using the 'fixed' value would allow authors to have fixed spacing of lines
> as is used traditionally in publishing. In extreme cases, collisions
> between lines might occur.

Also see the 'line-box-contain' property that is or was in the
draft.  What you want might be 'block' or 'block replaced' or
similar.

(I could imagine some authors wanting images to interrupt
line-spacing even when inline font variations don't, and others
wanting to go the other way.)

> It would also be useful to have a property to specify the dominant
> baseline. This is a reduced version of the property proposed in an older
> draft of the line layout spec:
> 
>   dominant-baseline: auto | alphabetic | ideographic | hanging | central
> 
> Here 'auto' would mean alphabetic for horizontal writing modes and central
> for vertical writing modes. For fonts with baseline information (e.g. a
> BASE table or it's equivalent) that information would be used to place text
> with respect to that baseline. For fonts lacking this information,
> appropriate defaults would be defined.

Given that this property is part of SVG and part of browsers, I
think we need to specify it eventually.

I described some of the history in
https://lists.w3.org/Archives/Public/www-svg/2010Apr/0150.html
although I'm not sure if we got it all right.

I think after some discussion we decided we want alignment-baseline
and baseline-shift to be subproperties of a shorthand
vertical-align, but dominant-baseline not to be reset by the
shorthand.  See:
https://lists.w3.org/Archives/Public/www-style/2014Jun/0108.html
https://lists.w3.org/Archives/Public/www-svg/2014May/0021.html

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
             What I was walling in or walling out,
             And to whom I was like to give offense.
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