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Re: [csswg-drafts] [css-conditional] Should CSS.supports() accept !important in the 2nd argument? (#5692)

From: Quentin via GitHub <sysbot+gh@w3.org>
Date: Tue, 03 Nov 2020 23:55:07 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-721436078-1604447706-sysbot+gh@w3.org>
I personally think it should be as it is in Firefox /  Chromium. Meaning:

CSS.supports("background: green !important"); // true
CSS.supports("background", "green !important"); // false

It's similar to function overloading. As the arguments are different. 

At `CSS.supports(conditionText)` the `!important` is seen as part of the condition and the whole term is evaluated as condition. 

At `CSS.supports(property, value)` the `!important` has no real affiliation to neither of the two arguements. As in this case the two arguments are parsed separately and the value  **_parses according to that property’s grammar_**.

> * If `property` is an ASCII case-insensitive match for any defined CSS property that the UA supports, **and** `value` successfully parses according to that property’s grammar, return `true`.
> * Otherwise, if `property` is a custom property name string, return `true`.
> * Otherwise, return `false`.

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