Re: [csswg-drafts] [css-fonts-4] [varfont] font format (src descriptor) function should be updated

Currently, in Edge and Firefox, extra arguments to format() are not 
treated as parse errors. This means that, in those browsers, you won't
 be able to make existing browsers (which don't understand variations)
 fall back correctly.

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");
}
```

In both examples, because these extra arguments are not treated as 
parse errors in those browsers, current versions of these two browsers
 will erroneously fetch the one marked as needing variations despite 
the browser not understanding variations. Therefore, neither of these 
fallback mechanisms will work properly in these two existing browsers.

However, in all browsers today, the following causes existing browsers
 to correctly ignore the variation font:

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

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Received on Tuesday, 4 October 2016 20:49:41 UTC