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[csswg-drafts] 'line-height: normal' definition should reflect reality of determining based on fonts

From: L. David Baron via GitHub <sysbot+gh@w3.org>
Date: Thu, 20 Apr 2017 01:45:02 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-222923110-1492652701-sysbot+gh@w3.org>
dbaron has just created a new issue for https://github.com/w3c/csswg-drafts:

== 'line-height: normal' definition should reflect reality of determining based on fonts ==
The [definition of `line-height: normal`](https://drafts.csswg.org/css2/visudet.html#propdef-line-height) says:
> Tells user agents to set the used value to a "reasonable" value based on the font of the element. The value has the same meaning as &lt;number>. We recommend a used value for 'normal' between 1.0 to 1.2. The computed value is 'normal'. 

This needs to explain what happens when font fallback occurs and multiple fonts are used.  Implementations use font metrics to get the normal line-height (at least some use external leading or line gap), and these metrics can be different in different fonts.  There may also be an interesting interaction with the [definition of the content height](https://drafts.csswg.org/css2/visudet.html#inline-non-replaced), which separately considers font fallback.

More research is needed here as to what implementations do and what they should do, in particular:
* what font metrics are used
* how the metrics from multiple fonts are combined, and whether this has an interaction with the computation of the content box height or whether it occurs entirely separately

/cc @litherum 

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/1254 using your GitHub account
Received on Thursday, 20 April 2017 01:45:09 UTC

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