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[csswg-drafts] [css-fonts-4] Extra unknown arguments to format() specifier should forbid font downloads/uses

From: litherum via GitHub <sysbot+gh@w3.org>
Date: Fri, 21 Oct 2016 20:15:00 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-184559366-1477080899-sysbot+gh@w3.org>
litherum has just created a new issue for 
https://github.com/w3c/csswg-drafts:

== [css-fonts-4] Extra unknown arguments to format() specifier should 
forbid font downloads/uses ==
When discussion the format() specifier with regards to font 
variations, we came across diverging behavior between different 
browsers.

There are two possible mechanisms (that I know of) for fallback:

```css
@font-face {
    ...
    src: url("file-novariations.otf") format("opentype");
    src: url("file-variations.otf") format("opentype", "variations");
}
```

and 

```css
@font-face {
    ...
    src: url("file-variations.otf") format("opentype", "variations"), 
url("file-novariations.otf") format("opentype");
}
```

Currently, Edge and Firefox would download the variation font even 
when though the browsers don't (currently) understand variations.

The spec states:

> The format hint contains a comma-separated list of format strings 
that denote well-known font formats. Conformant user agents must skip 
downloading a font resource if the format hints indicate only 
unsupported or unknown font formats.

This seems to imply that the format() identifier will be used if any 
of the arguments are known. Instead, in order to support modern and 
future font behaviors, web authors should be able to list the 
requirements that the browser needs to understand in order to use a 
font. Therefore, the format() identifier should be used if all of the 
arguments are known.

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/633 using your GitHub 
account
Received on Friday, 21 October 2016 20:15:11 UTC

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