safe-printable-inset META value proposal

[mstensho]

Proposed spec changes here: w3c/csswg-drafts#13190

Spec discussion: w3c/csswg-drafts#11395

[jcscottiii]

LGTM. I only have one question.

[jcscottiii]

Question: Is it worth it to enforce the usage of pixels here? (Or rather what's the risk if we don't enforce it?)

When new metadata is introduced, there's a risk of incorrect usage (e.g., typos, invalid values, or inappropriate units). For example, a value like content="2in" might be provided, even though the RFC suggests CSS pixels or points and discourages inches. The best way to mitigate this is to add automated checks. Other places that handled something similar:

• RFC 163 (web_features) added a lint to ensure its new metadata didn't get out of sync with test files
• RFC 158 (Variant name should be a non-zero length string) added a lint to forbid a problematic authoring pattern
• RFC 211 (Support testdriver.js in other test types) proposed a lint to enforce correct usage with reftest-wait.

[mstensho]

I was thinking a unitless value, which is why I'm suggesting pixels. But I suppose we could require units (and even allow centimeters, for all those rounding error fans out there) to be specified as part of the value instead?

[gsnedders]

Mostly my question is "how would we hook this up to the style engine", because somehow we have to go from the meta element to this impacting print style and output.

Most of the time we're using WebDriver to communicate with the browser; does it therefore make sense to add something to the WebDriver print command that specifies the safe printable inset? My gut is yes?

[mstensho]

Here's something I hacked together for testing.

https://chromium-review.googlesource.com/c/chromium/src/+/7415241

Does this answer your question?

[mstensho]

@gsnedders Are you asking whether we should add something to https://w3c.github.io/webdriver/#print-page ? I think that might be a good idea. It could be specified as a single inset value, or it could be a rectangle within pageWidth x pageHeight.

Is everything in centimeters here? That's rather bad, since they don't convert nicely to CSS pixels. But I suppose we need to follow suit.

[gsnedders]

@gsnedders Are you asking whether we should add something to https://w3c.github.io/webdriver/#print-page ?

Yes, which appears to be what the draft CL does. Can you please make a PR against WebDriver, and get consensus there first?

I think that might be a good idea. It could be specified as a single inset value, or it could be a rectangle within pageWidth x pageHeight.

It should allow both separately, I'd expect.

Is everything in centimeters here? That's rather bad, since they don't convert nicely to CSS pixels. But I suppose we need to follow suit.

Yes, which is… deeply unfortunate, I agree. Though to be fair, A4 paper doesn't convert nicely to CSS pixels either. :)

[mstensho]

@gsnedders Are you asking whether we should add something to https://w3c.github.io/webdriver/#print-page ?

Yes, which appears to be what the draft CL does. Can you please make a PR against WebDriver, and get consensus there first?

What's the name of the repo?

I think that might be a good idea. It could be specified as a single inset value, or it could be a rectangle within pageWidth x pageHeight.

It should allow both separately, I'd expect.

I really think one of them should be enough. But that can be discussed there.

Is everything in centimeters here? That's rather bad, since they don't convert nicely to CSS pixels. But I suppose we need to follow suit.

Yes, which is… deeply unfortunate, I agree. Though to be fair, A4 paper doesn't convert nicely to CSS pixels either. :)

Hey, A4 doesn't even convert nicely to centimeters. The height being 21cm * sqrt(2). :-p