Mike Taylor <miketa...@chromium.org> writes:
On 9/19/24 4:58 PM, Chromestatus wrote:
Contact emails
msten...@chromium.org
Explainer
https://github.com/mstensho/page-margin-boxes
Specification
https://drafts.csswg.org/css-page-3/#margin-boxes
Summary
Add support for page margin boxes, when printing a web document, or exporting
it as PDF. @page margin boxes
allows an author to define the contents in the margin area of a page, for
instance to provide custom headers and
footers, rather than using the built-in headers and footers generated by the
browser. A margin box is defined via an
at-rule inside a CSS @page rule. There are 16 rules defined, one for each
page margin box. There's one margin box
for each of the 4 corners on the page, and three (start, middle, end) for
each of the 4 sides. The appearance and the
contents of a margin box are specified with CSS properties inside the at-rule,
including the "content" property.
Counters are also to be supported, for page numbering. The specification
defines two special counter names:
"page" for the current page number, and "pages" for the total number of pages.
Blink component
Blink>Layout>Printing
TAG review
https://github.com/w3ctag/design-reviews/issues/918
TAG review status
Issues addressed
Risks
Interoperability and Compatibility
The spec defines the CSS counter names 'page' and 'pages'. Both are
accessible by the document's contents, so
that any element may use the counters to tell the current page number, or the
total number of pages. Documents
that use these counter names without being aware of this feature may be in
for a surprise. Most browsers offer to
generate some default headers and footers, and they are usually enabled by
default. If the document has margin
at-rules, they may come in conflict. We need some way of making sure that we
either use the browser-default
headers and footers, or the author-defined @page margins.
Can you clarify what you mean by "in for a surprise"?
I don't think I understand the compat implications of @page+
margin boxes here.
I'll remove this at chromestatus. It is no concern for now, since
counters in page / margin contexts will not interact with those of the
document. I.e. it's something we don't implement yet. The spec suggests
that they should interact, but it is vague, not too well thought through
(the spec forgets about parallel flows, for one), and the whole thing is
kind of weird, as counters are resolved in DOM tree order (i.e. the
precense of out-of-flow box, floats, etc.) do not affect the counter
scopes / values. Page / margin counters, on the other hand, need to be
resolved during layout. So we can revisit this later.
I wrote about this here (but how to fix the spec hasn't been discussed
yet):
https://github.com/w3c/csswg-drafts/issues/4760#issuecomment-1959298806
Also, do you have a plan for default header/footer conflicts w/
developer-provided ones?
Yes, sorry, forgot to update chromestatus again. Now fixed.
Most browsers offer to generate some default headers and footers, and
they are usually enabled by default. If the document has margin
at-rules, they may come in conflict and overlap if no action is
taken. Our solution: When a page has author-defined @page margin boxes
at the same edge of the page as a browser-default header or footer, the
browser-default ones will be suppressed (not displayed). This is in a
way similar to how the browser-default headers and footers are
suppressed when @page margins become too small for them to fit there
(with @page margin boxes, the author kind of takes control of the margin
area, and therefore there's nothing left for the UA, as if the margin on
that edge is zero).
Gecko: No signal (https://github.com/mozilla/standards-positions/issues/921)
WebKit: No signal (https://github.com/WebKit/standards-positions/issues/275)
Web developers: Positive
https://bugs.chromium.org/p/chromium/issues/detail?id=320370 currently has 98
stars.
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?
None
Debuggability
None
I think it's possible to emulate the print media via DevTools. Maybe there are
other possible debug modes to visually
represent these named margin boxes (as follow up work)?
Yes, we can emulate print media, as in "match @media print rules". But
that doesn't give us pagination. Getting devtools to paginate, so that
one could inspect the page boxes and margins (and margin box contents)
could indeed be useful. This is something that would have been useful
for years already, but with richer pagination support (like @page margin
boxes) it does become even more interesting.
There's crbug.com/40728089 for this.
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
WPT tests will be written and submitted while working on this feature.
Flag name on chrome://flags
None
Finch feature name
PageMarginBoxes
Requires code in //chrome?
False
Tracking bug
https://bugs.chromium.org/p/chromium/issues/detail?id=320370
Estimated milestones
Shipping on desktop 131
Shipping on Android 131
Shipping on WebView 131
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).
None
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5195769732923392?gate=6322213557108736
Links to previous Intent discussions
Intent to Prototype:
https://groups.google.com/a/chromium.org/g/blink-dev/c/ZCPkcu_dSF8
This intent message was generated by Chrome Platform Status.
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