[css-fonts-5]: define text-scale, legacy/scale keywords, env(preferred-text-scale) #12469
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| When the value of the [=text-scale=] content attribute is | ||
| <a for="text-scale">legacy</a> the user agent should set the initial font size | ||
| to 16px. The user agent may chose a different initial value, such as one based | ||
| on a user preference. The ''env()/preferred-text-scale'' value must be 1. |
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The value is always 1 on desktop, but not necessarily on mobile.
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Yeah, as in the Explainer, the env(preferred-text-scale) is the OS text scale on mobile. So if the user doubles their text scale, the value is 2, for example.
https://github.com/w3c/csswg-drafts/blob/main/css-env-1/explainers/env-preferred-text-scale.md#proposal
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Does this mean in the legacy mode that env(preferred-text-scale) may not be congruent with the font-size? As in font-size: medium will resolve to 16px even though the rest of the user's OS is at 24px because they have a text-scale 1.5? So an author cannot rely on calc(16px * env(preferred-text-scale)) resolving to the same CSS pixels as 1rem?
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That's correct, and is what happens in today's pre-<meta name="text-scale"> world.
We expect/hope that <meta name="text-scale" content="scale"> becomes best practice so that authors don't have to deal with today's inconsistencies, one of which is what you pointed out.
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| Note: It is expected that authors will use |
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@JoshTumath I'm interested to hear your thoughts on this paragraph :) As a non-author, I don't have a good sense of what authors are expected to do.
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If the meta tag is set to scale, authors would have no need to use calc(16px * env()). They can just use font-size: medium, since medium/the initial font size is now effectively that.
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font-size: medium will work for font sizes but presumably this also impacts ems & rems, such that 1rem will scale in proportion?
I think here I am simply trying to illustrate that authors might expect 16px to be the browsers font size and 16px * env() should (ideally?) resolve to the equivalent px units that 1rem * env() would.
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Oh I think I see what you mean. Yeah if the meta tag is set to the scale keyword, provided that the author doesn't change the root font-size, 1rem will always be equivalent to 16px * env(). I think I was confused by the phrasing of 'authors are expected to use it' since I wouldn't expect anyone to practically need to do that.
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Thanks so much for writing this!
Not sure if you already saw https://drafts.csswg.org/css-env-1/#text-zoom , which was the earlier iteration of the env() definition and pem.
| Text Scale {#text-scale-envs} | ||
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| <table dfn-type=value dfn-for="env()"> |
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Did you already crib everything appropriate from https://drafts.csswg.org/css-env-1/#text-zoom ?
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Didn’t even spot this, I’ll make sure everything is moved over and update this tomorrow.
| When the value of the [=text-scale=] content attribute is | ||
| <a for="text-scale">legacy</a> the user agent should set the initial font size | ||
| to 16px. The user agent may chose a different initial value, such as one based | ||
| on a user preference. The ''env()/preferred-text-scale'' value must be 1. |
There was a problem hiding this comment.
Does 'initial font size' need to be formally defined somewhere? My understanding is that the initial font size is the font-size: medium keyword. Maybe the definition of medium needs updating to formally define it as the UA setting by default in legacy mode and the UA setting * the OS text scale in scale mode.
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| Note: It is expected that authors will use |
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If the meta tag is set to scale, authors would have no need to use calc(16px * env()). They can just use font-size: medium, since medium/the initial font size is now effectively that.
This is an attempt at resolving #12380 by defining the
<meta name="text-scale">tag, how the UA responds to it (with thelegacyandscalekeywords) and defines theenv(preferred-text-scale)value and its relation to this.