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Re: [CSS21] Issues with inline formatting model (particularly 10.8)

From: Bert Bos <bert@w3.org>
Date: Mon, 31 Aug 2009 17:30:08 +0200
To: "www-style@w3.org" <www-style@w3.org>
Message-Id: <200908311730.08378.bert@w3.org>
I have an action to propose a clarification for the following (recorded 
as issue 121[1]):

On Sunday 01 March 2009, Anton Prowse wrote:
> 10.8.1, 'line-height' property
> (http://www.w3.org/TR/CSS21/visudet.html#propdef-line-height) :
>    # When an element contains text that is rendered in more than one
>    # font, user agents may determine the 'line-height' value
> according to # the largest font size.
>    #
>    # Generally, when there is only one value of 'line-height' for all
>    # inline boxes in a paragraph (and no tall images), the above will
>    # ensure that baselines of successive lines are exactly
> 'line-height' # apart.
> Issue 9a:  s/Generally/for example/

No, "generally" is correct, "for example" would not be right.

The height of the line boxes does not only depend on the value 
of 'line-height', but also on how much of an inline box is above or 
below the baseline, i.e., on 'vertical-align' and on the size of the 
descenders and ascenders in the different boxes. Especially if there 
are different fonts on a line, there is a good chance that one font 
extends further below the baseline than another, even if both have the 
same font size.

However, if the line is all in a single language it is likely that it 
only uses one font, hence the words "in general."

> Issue 9b:  s/tall images/inline replaced elements/

To be even more precise, the images referred to are inline replaced 
elements whose height and vertical alignment are such that their margin 
boxes fall completely within the line box height established by the 
surrounding elements.

But I'm not sure it is necessary to be very precise in this paragraph. 
It tries to give an intuition for what 'line-height' is roughly meant 
to do, without getting lost in details.

The sentence doesn't get worse by replacing "tall images" with "inline 
replaced elements" but it doesn't get better either. I don't think a 
change is necessary.

[1] http://wiki.csswg.org/spec/css2.1#issue-121

  Bert Bos                                ( W 3 C ) http://www.w3.org/
  http://www.w3.org/people/bos                               W3C/ERCIM
  bert@w3.org                             2004 Rt des Lucioles / BP 93
  +33 (0)4 92 38 76 92            06902 Sophia Antipolis Cedex, France
Received on Monday, 31 August 2009 15:30:52 UTC

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