Intent to Implement and Ship: break-before, break-after, break-inside CSS properties

[Emilio Cobos Álvarez]

Summary: Implement these properties to control breaks in the page, make
page-break-{before,after} legacy shorthands of those.

This work doesn't imply adding new layout functionality, just the style
system rejiggering to make us comply with the spec and be compatible
with other engines.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=775618

Link to standard: https://drafts.csswg.org/css-break/

Platform coverage: All platforms

Estimated or target release: Firefox 65

Preference behind which this will be implemented: None

Is this feature enabled by default in sandboxed iframes? Yes

DevTools bug: N/A, existing devtools support should be sufficient.

Do other browser engines implement this? Yes, since forever.
Fragmentation in general is not the most interoperable bit of the web
platform, though regarding these properties, the only thing we don't
support that they would is break-{before,after}: column, since we don't
restrict breaking to columns only.

web-platform-tests:
https://wpt.fyi/results/css/css-break/page-break-legacy-shorthands.html

See the following bugs for failures in other engines:

* https://bugs.chromium.org/p/chromium/issues/detail?id=906336
* https://bugs.webkit.org/show_bug.cgi?id=191803
* Didn't bother filing Edge bugs, given the news :(

Is this feature restricted to secure contexts? No, as other CSS bits.

-- Emilio

[Eric Shepherd (Sheppy)]

I just now saw this; as both a developer and as a writer on the MDN docs
team, I can tell you this will really be fantastic to have, and I can’t
wait! Not having control over breaks makes a lot of layout fail, especially
when trying to use multiple columns or grids to do layout.

On December 7, 2018 at 9:12:39 AM, Emilio Cobos Álvarez (emi...@crisal.io)
wrote:

Summary: Implement these properties to control breaks in the page, make
page-break-{before,after} legacy shorthands of those.

Eric Shepherd
Senior Technical Writer
MDN Web Docs <https://developer.mozilla.org/>
Blog: https://www.bitstampede.com/

[Emilio Cobos Álvarez]

On 12/21/18 7:23 PM, Eric Shepherd (Sheppy) wrote:
> I just now saw this; as both a developer and as a writer on the MDN docs
> team, I can tell you this will really be fantastic to have, and I can’t
> wait! Not having control over breaks makes a lot of layout fail, especially
> when trying to use multiple columns or grids to do layout.

FWIW Firefox allows you to control breaks as well (even before my
change) via the page-break-* properties (which we honored too for
non-paginated contexts).

But yeah, this should make the whole setup much clearer, and allow
people to write interoperable CSS too :)

-- Emilio

> On December 7, 2018 at 9:12:39 AM, Emilio Cobos Álvarez (emi...@crisal.io)
> wrote:
>
> Summary: Implement these properties to control breaks in the page, make
> page-break-{before,after} legacy shorthands of those.
>
>
> Eric Shepherd
> Senior Technical Writer
> MDN Web Docs <https://developer.mozilla.org/>
> Blog: https://www.bitstampede.com/

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