Add combined <*-percentage> data types from V&U to CSS 2.2

[SebastianZ]

CSS Values and Units Level 4 defines several combined percentage data types, which clarify how the percentages will be computed in the end.

Those <*-percentage> types should be incorporated into the CSS 2.2 specification or it should reference to V&U 4.

Sebastian

[fantasai]

They don't clarify any behavior. It's grammatical syntactic sugar. Not really worth fixing imho.

[SebastianZ]

They don't clarify any behavior. It's grammatical syntactic sugar.

They specify the behavior right in the syntax additionally to the prose, which allows to see at a glance how they are computed.

Not really worth fixing imho.

I could provide a patch if we agreed on it.

Quick overview of properties taking percentage values and whether they could be replaced by the new data types:

Property	Computed value	<*-percentage> values?
background-position	for the absolute value, otherwise a percentage	❌
bottom	if specified as a length, the corresponding absolute length; if specified as a percentage, the specified value; otherwise, 'auto'.	❌
font-size	absolute length	✅
height	the percentage or 'auto' (as specified) or the absolute length	✅
left	if specified as a length, the corresponding absolute length; if specified as a percentage, the specified value; otherwise, 'auto'.	❌
line-height	for and the absolute value; otherwise as specified	✅
margin-bottom	the percentage as specified or the absolute length	✅
margin-left	the percentage as specified or the absolute length	✅
margin-right	the percentage as specified or the absolute length	✅
margin-top	the percentage as specified or the absolute length	✅
max-height	the percentage as specified or the absolute length or 'none'	✅
max-width	the percentage as specified or the absolute length or 'none'	✅
min-height	the percentage as specified or the absolute length	✅
min-width	the percentage as specified or the absolute length	✅
padding-bottom	the percentage as specified or the absolute length	✅
padding-left	the percentage as specified or the absolute length	✅
padding-right	the percentage as specified or the absolute length	✅
padding-top	the percentage as specified or the absolute length	✅
pause-after	time	✅
pause-before	time	✅
right	if specified as a length, the corresponding absolute length; if specified as a percentage, the specified value; otherwise, 'auto'.	❌
text-indent	the percentage as specified or the absolute length	✅
top	if specified as a length, the corresponding absolute length; if specified as a percentage, the specified value; otherwise, 'auto'.	❌
volume	number	✅
width	the percentage or 'auto' as specified or the absolute length	✅

So, the values that can be safely replaced by <*-percentage>s are font-size, line-height, pause-after, pause-before and volume. For the ones with ❓ the descriptions suggest that it's up to the UA whether it computes them to percentage or absolute values.

Having said the above, I agree that it would only be a small improvement. So, if you still think it's not worth fixing - and besides you, @fantasai, I'd like to get feedback about that from @tabatkins - feel free to close this issue.

Sebastian

[tabatkins]

I think it's worthwhile to update CSS2.2 with this. 👍