Re: [csswg-drafts] [css-inline] A question for the procedure to compute the used value of "line-height" (#3749)

The logic for `line-height` described in css2.1 is know to be buggy.

It has been quite thoroughly reviewed and fixed, and css2.2 was made reliable. There remained some unsolved questions for`line-height: normal`, but it is a lot less wrong than what came before it.

However, for unrelated reasons (insufficiently careful edits had been made throughout the spec, so various parts were wrong, and which was which had become intractable), all changes to css2.2 had to be reverted to css2.1. We still haven't been able to re-apply all the known-to-be good changes.

This means the better definition of line height is currently in no spec at all. We should fix that, but until that happens, I recommend reading form the PR that did fix it at some point: https://github.com/w3c/csswg-drafts/pull/1993, while keeping an eye for possible issues. I'm aware of at least these: 
* https://github.com/w3c/csswg-drafts/issues/1254 (This one is partly solved, so you may want to skip the first half of the issue, but as the comments after https://github.com/w3c/csswg-drafts/issues/1254#issuecomment-296129092 show, there are still some unresolved points)
* https://github.com/w3c/csswg-drafts/issues/2418
* https://github.com/w3c/csswg-drafts/issues/1551

Based on all that, I am not sure that what you're trying to do is possible: unlike the other values of the property, `line-height: normal` does not result in single a height per element. Each text run may end up having a different height. To me, that means that returning 'normal' as a keyword makes more sense. Unless there's a compat constraint, I think CSSOM should be fixed accordingly (non-normal values should still be absolutized, but normal should stay as a keyword).

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Received on Wednesday, 20 March 2019 03:57:18 UTC