[css-logical] Unclear text regarding shorthands that encompass both logical and physical longhands

[Loirooriol]

https://drafts.csswg.org/css-logical/#box says

Shorthand properties that encompass both logical and physical longhands (such as the all shorthand) set omitted values first, and otherwise set the physical values last. For example, all: inherit will set all of the margin properties to inherit, but since the physical longhands are set last, the child’s margins will inherit from their physical counterparts in the parent.

This seems unintelligible to me:

• What are the "omitted values"? E.g. in all: inherit
• "otherwise" which condition?

[fantasai]

I think what this paragraph is trying to say is that

• if a shorthand explicitly sets a property value, this (obviously) takes priority over an implicit resetting
• also if it sets a value by omission by e.g. duplicating the previous value, this similarly takes priority
• if it resets some longhand to its initial value, this is lower priority than the explicit or implicit setting

Within the same priority, physical longhands are ordered last.

So for example, margin: logical 10px (should such a thing exist) would set all four logical longhands of margin, and they would take priority over the physical longhands that are in theory also reset by margin declarations. But all: initial or margin: reset-everything, the physical longhands are sorted later (higher priority) than the logicals.

I think that's what it's trying to say.

How it should actually say that, I'm not yet sure...

[tabatkins]

Shorthand properties that encompass both logical and physical longhands (such as the all shorthand) set omitted values first, and otherwise set the physical values last. For example, all: inherit will set all of the margin properties to inherit, but since the physical longhands are set last, the child’s margins will inherit from their physical counterparts in the parent.

If a shorthand property that encompasses both logical and physical longhands
(such as the 'all' shorthand)
explicitly assigns values to some of its longhands,
those longhands take precedence
over other longhands implicitly reset by the shorthand.
Within each group
(the explicitly set longhands, and the implicitly reset longhands),
physical longhands take precedence over logical longhands.
For example,
''all: inherit'' explicitly sets all of the margin properties to inherit,
so the physical margin longhands are set "last"
(overriding the logical ones),
and the child’s margins will inherit from their physical counterparts in the parent.

[tabatkins]

Example: say 'margin' had the ability to set all 8 longhands by explciitly naming the edge, like margin: 20px left, 30px inline-start;. In this case, left and inline-start would resolve their directions, realize that this is English so they're the same, and 'left' would win because it's physical. The rest of the sides would get reset to 0, with the physical ones reset last (unsure if this would be observable).

[fantasai]

I simplified the wording so it should hopefully not be confusing anymore. We'll want to revisit once we have more complicated shorthands, but I think this should do for now?

@Loirooriol What do you think?

[Loirooriol]

I don't remember if we settled this. In implementations, margin only expands to the physical longhands. But is it supposed to also set the logical ones (of course physical ones last)? To the initial value? Is this the "implicit resetting" that you mention?

If margin can expand to a different set of longhands depending on its value, then it's a mess. Because the value may not be known at parse time if there is a var(), but we must know which longhands need to be set to a pending-substitution value.

[Loirooriol]

In other words, is margin one of these "shorthand properties that encompass both logical and physical longhands"? Or does the sentence only apply to all for now?

[cdoublev]

Inheritance of each property is from its corresponding property on the parent. For example, although the inline-start margin of an rtl box is its right margin, margin-inline-start on this box will inherit the margin-inline-start of an ltr parent even though that happens to be the parent’s left margin.

margin-inline-start would inherit the parent margin-inline-start even if the parent box is rtl, isn'it? Fwiw, it confused me a bit. I mean of an ltr parent could be removed or reworded to "even though that happens to be the parent’s left margin (because the parent is ltr)".

And "inheritance of each property is from its corresponding property on the parent" seems to contradict this sentence in the next paragraph related to this issue about "logical shorthands":

[...] the child’s margins will inherit from their physical counterparts in the parent.

(Again, fwiw) "the child's margins will (directly or indirectly) inherit ..." might have helped me a bit.