CSS Validator suggestion: identify known properties with CSS 3 REC status

[rtonsing]

It would be nice to identify these and report them as known accepted styling, rather than reporting failure and expecting every user to know what can be ignored. Especially now that more are being added for accessibility.

For starters:

FAILED CSS Level 2.1 validation.
49.0: Value Error : display: “flex” is not a “display” value : flex
49.0: Property “justify-content” doesn't exist in “CSS level 2.1” but exists in “[css3]” : center
69.0: Property “overflow-x” doesn't exist in “CSS level 2.1” but exists in “[css3]” : auto
69.0: Property “overflow-y” doesn't exist in “CSS level 2.1” but exists in “[css3]” : auto

[windymilla]

I think it is correct to report them as errors if you do CSS level 2.1 validation. If you do level 3 validation, they won't be reported.

[rtonsing]

But neither one is the PG/DP standard:
https://www.pgdp.net/wiki/DP_Official_Documentation:PP_and_PPV/Post-processing_HTML5

Only use CSS3 that shows status=REC on this site, or that is on the following list:

So the choice is to see errors for styling that is actually allowed, or to not see errors for unallowed styling.
I just think it would be nice to have a tool that reports if the file CSS is "PG/DP compliant", this seems like a good place for it.

[windymilla]

I think being able to run any file through the W3C CSS validator as we currently do is valuable to have. Some people do that validation online, rather than through GG2, and I think it's good to match the online results.

I agree that we don't have a tool for checking the CSS is PG/DP compliant (nor checking that the HTML is compliant), which as you say is not the same as being valid CSS 2.1 or CSS3.

I don't think such a tool would be easy to write, and keep adjusting as our compliance rules change. The rules aren't (or haven't always been) as simple as saying that a particular attribute is permitted - sometimes, it is certain values that an attribute can have, or can be used for a certain purpose. My personal view is that PPers should know what is permitted by PG/DP, as documented on that wiki page.

If someone wanted to attempt to write such a tool, I'd be happy to consider it for inclusion in GG - we do try to report things that don't comply when we can.

[windymilla]

I also just thought of the fact that running ebookmaker on a file is part of ensuring it is compliant. If you run ebookmaker on a file that uses CSS that is not supported by ebookmaker, then it is reported at that stage. Perhaps that is sufficient, if the above tool is not practical to write?