Intent to Ship: Expose unprintable areas via CSS

[Morten Stenshorne]

Contact emails

mste...@chromium.org

Explainer

https://github.com/mstensho/unprintable-areas

Specification

https://drafts.csswg.org/css-page-3/#page-margin-safety

Summary

Printers usually have a small area at each of the four edges of a sheet of paper that they are not capable of marking reliably, usually due to the printer’s paper handling mechanism. The default page margins are expected to be bigger than these areas, but if authors set margins on their own, and even want to add @page margin boxes (e.g. for custom headers and footers), they need a way of telling where it's safe to print and not. The CSS descriptor `page-margin-safety` can be used to steer clear of such unprintable areas.

Blink component

Blink>Layout>Printing

Web Feature ID

Missing feature

Motivation

The browser itself has access to information about unprintable areas, so that it can place UA-generated headers and footers within the printable area, and also make the default page margins large enough to prevent loss of content. But once authors want to set their own page margins, or add page margin boxes (for e.g. custom headers and footers), the problem becomes clear, since this information isn't accessible via CSS. When developers want to place content near the paper sheet edges, be it due to small @page margins or page margin boxes (for custom headers and footers, for instance), without this change, the author would either have to hope for the best, or add some "reasonably large" margin to steer clear of potentially unprintable regions on the sheet.

Initial public proposal

https://github.com/w3c/csswg-drafts/issues/11395

TAG review

https://github.com/w3ctag/design-reviews/issues/1115

TAG review status

Issues addressed

Goals for experimentation

None

Risks

Interoperability and Compatibility

No information provided

Gecko: Positive (https://github.com/mozilla/standards-positions/issues/1258)

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/519)

Web developers: No signals

Other signals:

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 information provided

Debuggability

No information provided

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

No
Proposal here, filed some months ago: https://github.com/web-platform-tests/rfcs/pull/233 Still in review, but feedback is generally positive. It's about a `<meta name="safe-printable-inset" content="[inset-specifier]">` to be specified in WPT print tests. `inset-specifier` is a numeric value in centimeters, which is the largest unprintable inset among the four edges of the paper sheet. This is already implemented in Chromium's content_shell WPT testrunner, and a few tentative tests have been upstreamed. All pagination tests are handled by this testrunner in Chromium, since the headless Chrome testrunner doesn't handle pagination reliably.

Flag name on about://flags

No information provided

Finch feature name

CSSSafePrintableInset

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/368070327

Estimated milestones

Shipping on desktop	150
Shipping on Android	150
Shipping on WebView	150

Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).

No information provided

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5515971464527872?gate=6542696784855040

Links to previous Intent discussions

Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAKWZFm6j2Zg0UC78mnzF%2BRzeycQXzTPU_YpEZtAYAYQWNvgR8A%40mail.gmail.com

This intent message was generated by Chrome Platform Status.