W3C home > Mailing lists > Public > www-style@w3.org > February 2009

Re: vertical-align and line-height

From: David Hyatt <hyatt@apple.com>
Date: Thu, 26 Feb 2009 13:09:13 -0600
Cc: www-style@w3.org
Message-id: <A632D22F-F6CB-4632-B340-CECF71C03FC2@apple.com>
To: "L. David Baron" <dbaron@dbaron.org>
On Feb 26, 2009, at 12:22 PM, L. David Baron wrote:

> On Thursday 2009-02-26 17:30 +0100, Michael Jansson wrote:
>> I don't understand how the height of the single line is being  
>> computed
>> for the middle block element in Firefox and Opera. I would expect  
>> it to
>> be 100px, since none of the inline elements are taller than that.
>> However, I get a taller block in Firefox and Opera. I can also see  
>> that
>> there is actually two line boxes if I select the text in the  
>> browser. I
>> only expect one.
>
> Neither is taller than 100px, but they're not at the same position.
> The half-leading goes evenly on each side of the font, so the line
> is supposed to end up taller than 100px.
>
>> Second mystery is that the text is not being text-bottom aligned in
>> Firefox and Opera for the middle case. Intuitively, I wouldn't expect
>> setting the line-height to affect the vertical alignment. I would  
>> expect
>> case 2 and 3 to give the same result.
>
> This is because 'text-bottom' aligns the bottom of the box (which
> includes the half-leading, which is different sizes for different
> pieces of text) to the bottom of the parent's text.  (In this case,
> there isn't any text in the parent, but it still has metrics.)

Where is it specified that the half-leading should be included when  
doing text-bottom/text-top alignment?  I couldn't find this in the  
spec.  If a font can be thought of as being broken into half-leading +  
ascent + descent + half-leading, then WebKit is currently aligning to  
the top of the ascent when text-top is specified and the bottom of the  
descent when text-bottom is specified.  Is that wrong?  The result in  
WebKit makes more sense to me than what I'm seeing in Firefox and Opera.

dave
(hyatt@apple.com)
Received on Thursday, 26 February 2009 19:09:57 GMT

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