On 12/09/2016 06:14 PM, Florian Rivoal wrote:
On Dec 9, 2016, at 23:07, Michael A. Peters <mpet...@domblogger.net> wrote:

This was inspired by inspection of a style-sheet in the wild that uses 
screen-width to try and reduce bandwidth needs of mobile devices.

I like the concept, but very often I use my mobile devices where bandwidth 
doesn't matter and my laptop via a mifi where bandwidth does matter.

I would like a CSS media query for bandwidth so that I can reduce how many 
webfonts are used in low bandwidth scenarios. It seems browsers are already 
smart enough to only download a font defined by @font-face if they need it, so 
it only needs to be done where the font is used, e.g.

It's been considered before, and that approach will not work. Media queries are 
the wrong tool for this. Neutrality / bias warning: I'm co-editor of the Media 
Queries spec.

Media queries, by design, will switch instantly when the environment changes, 
stop applying the old styles, and start applying the new ones. So if you finish 
loading a page on your phone in your home wifi with the high-res and heavy 
assets, start reading, then walk outside into 3G, you'll discard the high res 
assets and start loading the low res ones. And if you're driving / riding a 
train in and out of tunnels, you'll toggle between high and low (or low and 
terrible) constantly, and never manage to finish loading anything, all while 
using copious amounts of bandwidth. This isn't a bug, this is how Media Queries 
work, and is the right thing to do for things where media queries are the right 
tool. If that's not what you want, what you want isn't a media query.

The right approach is something like srcset[1], the source element[2], or 
image-set()[3]: instead of switching between one variant or another based on a 
hard criteria, you provide the UA with all the variants you have, and let it 
switch intelligently.

Of course, these are UA based heurisitics, it is certainly possible that the UA 
will make poor decisions sometimes, but that's a lot better than the guaranteed 
bad behavior you'd get with Media queries.

For fonts, there isn't currently an equivalent mechanism, but we could think of 
adding qualifiers either the @font-face that declares the font, or font-family 
that tries to use it, to indicate that certain fonts are must-have, while 
others are optional things that are fine to skip in case of bad bandwidth or 

There's already one proposal in that direction, although it hasn't received 
much attention lately: https://tabatkins.github.io/specs/css-font-display/

Finally, while you're free to talk about this anywhere you like, traditionally 
the best forum for CSS related topics is the CSSWG, either through its 
github[4] or its mailing list[5].


[1] https://html.spec.whatwg.org/multipage/embedded-content.html#attr-img-srcset
[3] https://drafts.csswg.org/css-images-3/#image-set-notation
[4] https://github.com/w3c/csswg-drafts/issues
[5] https://lists.w3.org/Archives/Public/www-style/

I've thought about this for several hours now and I have to concede, a media query is not the right place for this.

I don't think @font-face is either as it would cause backwards compatibility problems, and there are other issues with @font-face.

For example, when I use @font-face to define a bold font face, then when I declare that font for strong I have to explicitly tell the CSS to use the normal weight or the browser applies a fake bold to the already bold font.

Perhaps what is needed is an @font-family declaration that can be used to specify the various variants of a font.

Then when the font-family is called and something like a strong tag is encountered, the browser will use the defined bold variant if it exists and apply fake bold to the roman font if it does not.

If variants within @font-family are declared optional, then the browser does not have to include it.

That would solve another problem with my media query solution. If the page was ever loaded when bandwidth isn't an issue, it may have the optional woff2 files in cache.

It would then be able to use them even in low bandwidth, since it already had them, and only apply fake variant instead if it doesn't have it in cache and it is flagged as optional.

I'll think about this some more, then join the right list for it and put the revised idea there.

But for now I have to concede media query is the wrong approach.

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