[css-values] Change MAY into MUST regarding calc() on table

[xiaochengh]

#94 has made a resolution that certain calc() mixing both lengths and percentages MUST be treated as auto instead of MAY. Updating spec accordingly.

Relevant WPT are updated in https://chromium-review.googlesource.com/c/chromium/src/+/1832619.

[davidsgrogan]

At first glance the simple s/MAY/MUST/ seems to prohibit treating calc(10% + 0) as 10%.

emilio: what about calc(10% + 0)?
... that's simplifies to 10% in all browsers
Rossen: yes we've resolved that previously

[emilio]

That is a good point... #3482 (comment) seems to imply it should be treated the same:

calc(% + 0px) vs calc(%)

Sure. There's no case in which these two should be different. Lengths never have magical behavior, so adding it to a % shouldn't add any complications, and in the rare cases where length+% is different than just resolving the % and adding the two together (bg-position), a 0px length is still a no-op.

[xiaochengh]

Suggested change

	math expressions mixing both percentages and lengths for widths and heights on
	math expressions mixing both percentages and non-zero lengths for widths and heights on

According to #3482, it is safe to drop 0 length from <length-percentage>. Then how about making it explicit here?

[davidsgrogan]

According to #3482, it is safe to drop 0 length from . Then how about making it explicit here?

SGTM. As far as I can tell, the resolution from #3482 isn't in any spec. Are you proposing to add it here explicitly?

[xiaochengh]

@tabatkins Could you help?

I'm not familiar with the editing process. What should we do here?

[FremyCompany]

LGTM (but I'm not the editor of that spec)