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Re: [csswg-drafts] [css-logical] Flow-relative syntax for `margin`-like shorthands (#1282)

From: Oriol Brufau via GitHub <sysbot+gh@w3.org>
Date: Fri, 30 Nov 2018 17:21:07 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-443275428-1543598466-sysbot+gh@w3.org>
The problem is that it's bad if you need to know whether the shorthand will expand into physical OR logical longhands at specified-value time, but this depends on the computed value of `flow-mode` (or `writing-mode` in your second idea, but this would be too hacky).

However, something similar to https://drafts.csswg.org/css-variables-1/#variables-in-shorthands could be done:
 - The shorthand expands into all physical AND logical longhands (the order does not matter)
 - The specified value of the longhands is set to a special, unobservable to authors "pending-logical-resolution value"
 - This value must then be cascaded as normal
 - At computed-value time, the shorthand must be parsed and the longhands must be given their appropriate values at that point according to the computed value of `flow-mode`.
 - Pending-logical-resolution values must be serialized as the empty string, if an API allows them to be observed.

It think this would more or less work, but it would be a breaking change:

```js
element.style.margin = "1px 2px 3px 4px";
element.style.marginTop;
```

Currently it produces `"1px"`, but would become `""` because at specified-value time it's not known whether the `1px` will be set to `margin-top` or `margin-block-start`.

So IMO it would be simpler and less problematic to decide between logical or physical via syntax instead of via the computed value of another property.

-- 
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Received on Friday, 30 November 2018 17:21:09 UTC

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