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Re: [csswg-drafts] [css-color-adjust-1] What happens with multiple <meta>s? (#3846)

From: CSS Meeting Bot via GitHub <sysbot+gh@w3.org>
Date: Wed, 24 Jun 2020 16:22:12 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-648923121-1593015731-sysbot+gh@w3.org>
The CSS Working Group just discussed `[css-color-adjust-1] What happens with multiple <meta>s?`, and agreed to the following:

* `RESOLVED: Have color scheme use the same meta scheme as theme color.`
* `RESOLVED: Ask HTML to specify this and move out of CSS specs`

<details><summary>The full IRC log of that discussion</summary>
&lt;dael> Topic:  [css-color-adjust-1] What happens with multiple &lt;meta>s?<br>
&lt;dael> github: https://github.com/w3c/csswg-drafts/issues/3846<br>
&lt;dael> TabAtkins: Have the &lt;meta> name and equals color shceme. Page declares color on root element in way that comes in early on page w/o requiring load css file. Might have noticable delay while page has not great canvas background<br>
&lt;dael> TabAtkins: What happens if you spec same meta multiple times<br>
&lt;dael> TabAtkins: Several options. Reviewing HTML where you can have several metas all possible patterns exist. No consistency. Things that are most similar, esp theme-color meta which adjusts color of UI on page has a specific behavior. First one that's parsable wins and if things are dynamically updated we re-run selection algo<br>
&lt;dael> TabAtkins: Fine for me.<br>
&lt;dael> TabAtkins: Does mean you don't have standard css fallback behavior where can spec newer color and a fallback. Trade off is you don't have to wait several packets to make sure there's no additional metas.<br>
&lt;dael> TabAtkins: Trade-off is fine since this is designed to give a value as soon as possible<br>
&lt;dbaron> You can do the CSS-like fallback behavior by doing it in the reverse order, too, no?<br>
&lt;dael> TabAtkins: Suggest we unify with theme-color meta. First things that parses in the document with the restrictions listed by Dominik.<br>
&lt;TabAtkins> https://github.com/w3c/csswg-drafts/issues/3846#issuecomment-577337007<br>
&lt;TabAtkins> last option<br>
&lt;cbiesinger> s/Dominik/Domenic/<br>
&lt;dael> Rossen_: You said...we prefer the first one if it parses and subsiquent do not trigger restyle. What about nested documents? In an iFrame do I need to know there was already match in primary doc?<br>
&lt;dael> TabAtkins: In terms of selecting a meta no communication. Applying theme colors I don't know if we inherit into other docs but if we do it works same as CSS. iframe selection own meter b/c separate document<br>
&lt;dael> Rossen_: Okay. If based on main there was potentially some info leaked<br>
&lt;dael> Rossen_: Second question, have you considered opposite where we treat it more like style and continue to consider everything? What's main reason to reject it?<br>
&lt;dael> TabAtkins: Not crazy. Reason to reject is first nice to reuse similar modal. Second the purpose of this feature is get a value as fast as possible without making browser delay to get more stuff. Being able to see first and know it's the color to display I think is valuable b/c no need to run trade offs about should I delay paint while I wait to see if there's overrides.<br>
&lt;dael> TabAtkins: If you need multi values due to new color schemes you can just put a style tag in. It's a bit more verbose and depending on your exact csp set up it may not work<br>
&lt;dael> TabAtkins: Addressing exact use case I think we lean toward take first one that matches over benefit of fallback<br>
&lt;dael> Rossen_: Okay. Is more restrictive model. I can't tell if it will be final, but we can also if there are compelling cases to allow subsiquent metas we can scale out model.<br>
&lt;dael> TabAtkins: Ultimately though we talked aout more color schemes I don't think there's any plans now to add them. At least for next several years we're stuck with 2 so we don't have to worry about it. If it changes calculus is different<br>
&lt;dael> astearns: dbaron pointed out if you're concerned about not parsing you can put in reverse order to get fallback order<br>
&lt;dael> TabAtkins: Yeah. Yeah. You can do that. It does have same fallback as CSS. dbaron is right. You put 2 metas, first has new syntax. Modern browsers find the first and use, old can't parse, skip, and than use old. Have fallback, opposite order of CSS<br>
&lt;dael> dbaron: Only weird is it's non-conformant<br>
&lt;dael> TabAtkins: In older browser, yeah<br>
&lt;dael> dbaron: Conformance requirement says it's not allowed to have multiple. Maybe that's not great<br>
&lt;dael> TabAtkins: Agree, value to loosen it<br>
&lt;dael> astearns: Any more comments?<br>
&lt;dael> astearns: Comment from Rune about moving it to HTML spec<br>
&lt;dael> TabAtkins: Agree. Need to settle and than tell HTML what to put in.<br>
&lt;dael> TabAtkins: I think it's abstract theme-color algorithm and have it apply to both<br>
&lt;dael> astearns: Prop: Have color scheme use the same meta scheme as theme color.<br>
&lt;dael> astearns: Perhaps changing conformance requirement to both. Recommend this as change to HTML spec<br>
&lt;dael> TabAtkins: Yep<br>
&lt;dael> astearns: Objections to the scheme?<br>
&lt;dael> RESOLVED: Have color scheme use the same meta scheme as theme color.<br>
&lt;dael> astearns: Obj to have this spec entirely in HTML an not our specs?<br>
&lt;dael> RESOLVED: Ask HTML to specify this and move out of CSS specs<br>
&lt;dbaron> it might still be worth linking to the HTML spec to point it out<br>

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Received on Wednesday, 24 June 2020 16:22:14 UTC

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