[css-backgrounds-4] How to set declarations of background-position containing a logical keyword?

[cdoublev]

Context

• the grammar of background-position as a shorthand is still under discussion
• there is some browser support of background-position-x/background-position-y
• there does not seem to be a pressing need to implement this feature

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When the specified value includes a logical keyword, the text does not seem to know what it should exactly happen yet:

Issue 2: Specify the value assignment in more detail. Should expand just like Level 3.

Issue 3: Specify what happens to set of properties that are not set. Maybe they’re just not set?

https://drafts.csswg.org/css-backgrounds-4/#propdef-background-position

Logical longhand declarations must be added after physical longhand declarations, isn't it? And physical longhand declarations must be added after logical longhand declarations if physical keywords are specified.

If I am not mistaken, step 3.4.2 of serialize a CSS declaration block would need to be changed if the set of longhands that is not explicitly declared is not reset to its initial value:

2. If all properties that map to shorthand are not present in longhands, continue with the steps labeled shorthand loop.

For example: if shorthand maps to longhands included in a logical property group, and all longhands of the same mapping logic have a declaration in longhands (excluding longhand declarations that do not map to shorthand) that come after any other declaration with another mapping logic, continue with the procedure.

A similar check would be required in the procedure of style.getPropertyValue().

But what is the benefit of, I guess, preserving longhands declarations that would have been set before setting the shorthand with values for longhands that follow a different mapping logic?