LGTM2
/Daniel
On 2022-09-21 07:39, Yoav Weiss wrote:
LGTM1 - thanks for following up on the TAG's feedback!
On Tue, Sep 20, 2022 at 1:47 AM Dominik Röttsches <dr...@chromium.org>
wrote:
Contact emails
dr...@chromium.org
Explainer
https://github.com/w3c/csswg-drafts/blob/main/css-conditional-5/font-tech-format-explainer.md
Specification
https://www.w3.org/TR/css-conditional-5/#at-supports-ext
Summary
The font-tech() and font-format() are extensions to the @supports
rule CSS Conditional Syntax enable declarative and programmatic
access to feature detection of font stack features. Using these
conditions together with @supports allow progressive enhancement
of content depending on font format support. In particular with
UAs differing in support for color font formats, this is useful
for including color font style rule and @font-face definitions
only if the user agent supports it. Using JS CSS.supports() calls
this is also the first ergonomic way of testing for font stack
capabilities on the web without UA sniffing or canvas pixel
readback as in Chromacheck (https://pixelambacht.nl/chromacheck/).
This feature is closely related to the @font-face src: descriptor
syntax extension which was recently discussed and LGTM'ed here
<https://groups.google.com/a/chromium.org/g/blink-dev/c/_9k-Ne8FRu4>:
- the same font format and technology keywords are used and
synchronized between these two features.
*Motivation*
While font files look the same from the outside in their mime type
and file signature, they may contain information that requires
specific features of the UA's font stack. If an author wants to
progressively enhance their site depending on font format
capabilities of the UA, feature detection is needed. This feature
here provides such a capability on the client side in two ways,
declaratively in CSS, or programmatically in JS using
CSS.supports(). Examples:
* If OpenType variations are supported, I want to use a set of
different style rules than when variations are not available
* If color font support is available, I want to enhance my site
with a colorfonts plus style rules affecting other parts of my
page.
Blink component
Blink>Fonts
<https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3EFonts>
TAG review
https://github.com/w3ctag/design-reviews/issues/666
TAG review status
Issues addressed
Risks
Interoperability and Compatibility
/Gecko/: In development
(https://github.com/mozilla/standards-positions/issues/563#issuecomment-1224131600)
Implemented behind flag and standards position concluded with
positive stance towards this feature. Jonathan Kew plans to ship
this soonish and in any case in sync with COLRv1 support.
/WebKit/: From the standards discussion on this, my take-away of
the discussion with Myles is that the feature is useful, but Myles
suggests to ship it only in combination with @else
<https://github.com/w3c/csswg-drafts/issues/6520#issuecomment-947346133>
- my position is that @else is not essential for this feature to
provide value.
/Web developers/: Positive Feedback we received from partners is
that robust feature detection for this feature is a requirement
and helps activation of usage of color fonts. More info available
internally. (See previous I2S for tech() and format() in the src:
descriptor of font-face)
/Other signals/:
Ergonomics
This feature is intended for situations where the progressive
enhancement choice is made client side. Feature detection on the
server side, at the time for example the UA makes a request for a
style sheet is out of scope for this proposal. In those
situations, UA sniffing on the server side is still performed on
the server based on request headers and user-agent string - which
may be addressed by font feature client hints in the future.
Activation
Low: If this feature is not supported, the respective CSS styles
are not included, so the progressive enhancement fails, which is
the nature of this approach. If CSS.supports() calls are failing
because they are not available, then the program logic trying to
feature detect font stack capabilities, may need to resort to
other methods of testing font support, for example through Canvas
pixel probing or hardcoded UA lists.
WebView application risks
Does this intent deprecate or change behavior of existing APIs,
such that it has potentially high risk for Android WebView-based
applications?
No.
Debuggability
Equivalent to other @supports debugging.
Will this feature be supported on all six Blink platforms
(Windows, Mac, Linux, Chrome OS, Android, and Android
WebView)?
Yes
Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?
Yes, tests were added by Mozilla's Jonathan Kew initially while
developing support for this feature in Gecko with additional tests
and modifications to them when I developed the feature behind a flag.
Flag name
chrome://flags/#enable-experimental-web-platform-features
Requires code in //chrome?
False
Tracking bug
https://bugs.chromium.org/p/chromium/issues/detail?id=1255685
Sample links
https://github.com/w3c/csswg-drafts/blob/main/css-conditional-5/font-tech-format-explainer.md#use-case-1---progressive-enhancement-with-color-fonts
Estimated milestones
108
Anticipated spec changes
Additional keywords may be added in the future.
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5155718374621184
This intent message was generated by Chrome Platform Status
<https://chromestatus.com/>.
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