[Webkit-unassigned] [Bug 226461] REGRESSION(r266674) Fixed positioned content not displayed

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=226461

--- Comment #7 from Oriol Brufau <obrufau at igalia.com> ---
Well, for me there are 2 reasons that it doesn't show up.

The first one is that _.clientPushAPI is somehow null, and then it aborts. Not sure where this clientPushAPI comes from, but seems unrelated to logical properties. Maybe it's just a thing of my WebKitGTK and it's not null in Safari.

And the 2nd reason is indeed caused by logical properties. Just run

(function() {
  var prompt = document.createElement('div');
  prompt.style.all = "initial";
  prompt.style.position = "fixed";
  prompt.style.bottom = 0;
  prompt.style.left = 0;
  prompt.textContent = "foobar";
  document.body.appendChild(prompt);
})();

First, 'all' sets all longhands in lexicographic order, so 'bottom' comes before 'inset-block-end'.

Then it sets 'bottom: 0', but this just updates the value in-place.

So the property is still overridden by 'inset-block-end: initial'.

Solution: when setting a property value, if afterwards there is another property that belongs to the same logical property group but has a different mapping logic, remove the original property and set the new value at the end.
https://drafts.csswg.org/cssom/#set-a-css-declaration

I don't think WebKit has the concept of logical property groups and mapping logic. That will need to be implemented first.

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