Intent to implement and ship: Overflow media queries

[Emilio Cobos Álvarez]

Summary: More explicitly expose the kind of handling for overflowing
content in media queries. Using a media expression instead of the print
media type allows for more flexibility, see the bug description.

Implementation wise, we already expose the same kind of information via
@media print right now, given we don't have any kind of built-in EBook
mode or something like that.

A volunteer sent patches for this, and I see no reason not to take them,
unless somebody objects here. Thanks a lot quasicomputational@! :)

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1422235

Link to standard:
https://drafts.csswg.org/mediaqueries-4/#mf-overflow-inline
https://drafts.csswg.org/mediaqueries-4/#mf-overflow-block

Platform coverage: all

Estimated or target release: 66

Preference behind which this will be implemented: None

Is this feature enabled by default in sandboxed iframes: Yes

DevTools bug: N/A, existing devtools features should cover this.

Do other browser engines implement this? No, we'd be the first ones
implementing this part of the spec, but I think it's uncontroversial.
The spec author was the one that filed the bug requesting
implementation, so spec-wise the feature should be stable as well.

web-platform-tests: Minimal parsing tests are being added to:

https://wpt.fyi/results/css/mediaqueries/test_media_queries.html

Unfortunately WPT has no way to test print preview or pagination right
now so the rest of reftests are Gecko-only.

Is this feature restricted to secure contexts? No, same as all other
media expressions.

[James Graham]

On 23/12/2018 10:59, Emilio Cobos Álvarez wrote:
> web-platform-tests: Minimal parsing tests are being added to:
>
>   https://wpt.fyi/results/css/mediaqueries/test_media_queries.html
>
> Unfortunately WPT has no way to test print preview or pagination right
> now so the rest of reftests are Gecko-only.

Mind filing an issue on the wpt repo about the inability to test these
features? It seems like something we could at least investigate,
although I don't think there's currently any cross-browser API
(including via e.g. WebDriver) for getting paginated layout.

[Emilio Cobos Álvarez]

I think this is covered already by:

https://github.com/web-platform-tests/wpt/issues/7760

We have reftest-paged for this and also a programatic (yet not ideal)
way to test print preview:


https://searchfox.org/mozilla-central/rev/0ee0b63732d35d16ba22d5a1120622e2e8d58c29/layout/base/tests/chrome/printpreview_helper.xul#26

-- Emilio

[fantasai]

On 12/23/18 2:59 AM, Emilio Cobos Álvarez wrote:
> Summary: More explicitly expose the kind of handling for overflowing content in media queries. Using
> a media expression instead of the print media type allows for more flexibility, see the bug
> description.
>
> Implementation wise, we already expose the same kind of information via @media print right now,
> given we don't have any kind of built-in EBook mode or something like that.
>
> A volunteer sent patches for this, and I see no reason not to take them, unless somebody objects
> here. Thanks a lot quasicomputational@! :)
>
> Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1422235
>
> Link to standard:
>   https://drafts.csswg.org/mediaqueries-4/#mf-overflow-inline
>   https://drafts.csswg.org/mediaqueries-4/#mf-overflow-block
>
> Platform coverage: all
>
> Estimated or target release: 66
>
> Preference behind which this will be implemented: None
>
> Is this feature enabled by default in sandboxed iframes: Yes
>
> DevTools bug: N/A, existing devtools features should cover this.
>
> Do other browser engines implement this? No, we'd be the first ones implementing this part of the
> spec, but I think it's uncontroversial. The spec author was the one that filed the bug requesting
> implementation, so spec-wise the feature should be stable as well.

General CSSWG policy is that any spec in CR has the consensus of the CSSWG
to be implemented and shipped.
“Once a specification reaches the Candidate Recommendation stage,
implementers should release an unprefixed implementation of any
CR-level feature they can demonstrate to be correctly implemented
according to spec, and should avoid exposing a prefixed variant
of that feature.” -- https://www.w3.org/TR/CSS/#testing

Media Queries Level 4 is in CR, so anything there is good to go.

~fantasai