Re: [csswg-drafts] [css-backgrounds] Number of layers in getComputedStyle results (#4135)

The CSS Working Group just discussed `Number of layers in getComputedStyle results`, and agreed to the following:

* `RESOLVED: Have the computed value of the background / image layer properties match the number of items in the specified value`
* `RESOLVED: Apply the rule for computed value list length of background properties to all other similar list repeating properties like masking, transitions, animations.`

<details><summary>The full IRC log of that discussion</summary>
&lt;heycam> Topic: Number of layers in getComputedStyle results<br>
&lt;heycam> github: https://github.com/w3c/csswg-drafts/issues/4135<br>
&lt;heycam> fantasai: there's some inconsistency in how many layers we put in these properties<br>
&lt;heycam> ... the suggestion is to take the computed value's list length<br>
&lt;heycam> ... if you have a long list for background-image, but a short list for background-position<br>
&lt;heycam> ... when you return getCS, do you use the original list length, or the number of images?<br>
&lt;heycam> ... I think we should use the number of values specified<br>
&lt;heycam> oriol: in Chromium, this information is lost in the computed style<br>
&lt;heycam> ... inheriting onto children, the information is not inherited<br>
&lt;heycam> TabAtkins: this is a Chrome bug<br>
&lt;heycam> ... we should do the right thing and match Firefox here<br>
&lt;heycam> fantasai: let's do that, and clarify the Backgrounds spec<br>
&lt;heycam> ... which just says list, not how many items<br>
&lt;fantasai> file:///home/fantasai/w3c/csswg/css-backgrounds-3/Overview.html#background-repeat<br>
&lt;heycam> ... so clarify to the specified number of items<br>
&lt;fantasai> Computed value: list, each item a pair of keywords, one per dimension<br>
&lt;fantasai> list -> "list of the specified number of items"<br>
&lt;fantasai> or something<br>
&lt;fantasai> list (of the number of items specified)<br>
&lt;heycam> RESOLVED: Have the computed value of the background / image layer properties match the number of items in the specified value<br>
&lt;heycam> dbaron: other properties?  transitions<br>
&lt;heycam> ... all of these cases are repeated lists where you key off one list to determine what happens<br>
&lt;fantasai> s/value/value of the property itself, not the reference property/<br>
&lt;heycam> ... but I think in all cases that is the right thing<br>
&lt;heycam> dbaron: transitions used to have two different types of list repeating<br>
&lt;heycam> TabAtkins: that's in V&amp;U now<br>
&lt;fantasai> Not in Values. Values just as hhttps://drafts.csswg.org/css-values-4/#combining-values<br>
&lt;fantasai> https://drafts.csswg.org/web-animations-1/#animating-properties<br>
&lt;heycam> dbaron: backgrounds, masking, transitions, animations<br>
&lt;heycam> ... sounds like the relevant list here<br>
&lt;fantasai> ACTION: fantasai fix animation types of CSS Backgrounds<br>
&lt;heycam> RESOLVED: Apply the rule for computed value list length of background properties to all other similar list repeating properties like masking, transitions, animations.<br>
</details>


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Received on Wednesday, 22 January 2020 15:47:43 UTC