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[css-color-adjust-1] Move color-scheme meta to HTML #3846 #5540

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Sep 24, 2020
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[css-color-adjust-1] Move color-scheme meta to HTML #3846 #5540

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e5035fe
[css-color-adjust-1] Move color-scheme meta to HTML
lilles Sep 23, 2020
8f47ae4
fixup! [css-color-adjust-1] Move color-scheme meta to HTML
lilles Sep 24, 2020
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46 changes: 5 additions & 41 deletions css-color-adjust-1/Overview.bs
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Expand Up @@ -225,6 +225,11 @@ Opting Into a Preferred Color Scheme: the 'color-scheme' property {#color-scheme
To ensure particular foreground or background colors,
they need to be specified explicitly.

Note: [[HTML]] specifies a
<a href="https://html.spec.whatwg.org/multipage/semantics.html#meta-color-scheme">color-scheme</a>
<{meta}> tag which can be used to set the color-scheme on the root element as
a [[css-cascade-4#preshint|non-CSS presentational hint]].

Note: Earlier versions of this property also defined an <css>only</css> keyword
to be specified alongside a preferred color scheme,
indicating a stronger author preference.
Expand Down Expand Up @@ -260,47 +265,6 @@ Effects of the Used Color Scheme {#color-scheme-effect}
via elements intended for graphics
(such as <{img}> elements embedding an SVG document).

The "color-scheme" <{meta}> value {#color-scheme-meta}
---------------------------------

To aid user agents in rendering the page background with the desired [=color scheme=] immediately
(rather than waiting for all CSS in the page to load),
a 'color-scheme' value can also be provided in a <{meta}> element.

If any <{meta}> elements are [=inserted into a document=] or [=removed from a document=],
or existing <{meta}> elements have their <{meta/name}> or <{meta/content}> attributes changed,
user agents must run the following algorithm:

<div algorithm="find the color-scheme meta">
1. Let |candidate elements| be the list of all <{meta}> elements that meet the following criteria,
in [=tree order=]:

* the element is [=in a document tree=]
* the element has a <{meta/name}> attribute,
whose value is an [=ASCII case-insensitive=] match for <code>color-scheme</code>
* the element has a <{meta/content}> attribute,
whose value is not the empty string
* the element is a child of the [=the head element=] of the document

2. For each |element| in |candidate elements|:
1. If |element|’s <{meta/content}> attribute's value
[=CSS/parses=] as a <'color-scheme'> value,
treat that value as a declaration of the 'color-scheme' property on |element|’s [=tree/root=],
cascaded as a [[css-cascade-4#preshint|non-CSS presentational hint]].
Then return.

Note: Because these rules check successive elements until they find a match,
an author can provide multiple such values
to handle fallback for legacy user agents.
Opposite how CSS fallback works for properties,
the multiple <{meta}> elements must be arranged
with the legacy values <em>after</em> the newer values.
</div>

Issue(#3846): This algorithm favors the first <{meta}>,
to allow for ASAP rendering with a chosen color scheme.
Is that the desired behavior?


Forced Color Schemes: the 'forced-color-adjust' property {#forced}
====================
Expand Down