[css-backgrounds-4] Initial value of 'background-position-y' should be 'top'

[kuoe0]

I found the initial value of background-position-y defined in spec is wrong. I think it should be top.

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

[LeaVerou]

Yup, that's certainly a spec bug. For those wondering: The current value listed is ...left 😂

[cdoublev]

This has been fixed in eca3884 therefore this issue can be closed, but I would like to take this opportunity to ask why the initial background-position-inline|block value is not start (ie. the position where you start reading) instead of not applicable (initial value comes from physical property)?

[SebastianZ]

You're right. All other specs that define logical properties also specify their initial values. So I went ahead and changed it to 0% in 39e7612. I chose 0% rather than start because all other logical properties also use the initial value of their physical counterparts.

Sebastian

[cdoublev]

Thanks. Indeed, resolving the writing mode at specified value time seemed problematic to me. For example, when background: center appears in a style sheet, background-position-block|inline must reset to its initial value.

Other logical properties seem to be mostly defining distance values, not a position like background-position, mask-position, or scroll-start. The latter has scroll-start-block|inline defined with auto as its initial value but there is no associated definition. Shorthand encompassing both flow-relative and physical properties should map to their physical sub-properties after their flow-relative sub-properties, therefore the initial value of the latter will not affect the formers. But anyway, 0% is fine.