[css-masking-1] Allow permutation in mask-border-slice

[cdoublev]

I think && was lost in this commit.

Name: mask-border-slice
Value: [ <number> | <percentage> ]{1,4} fill?

See the border-image-slice property [CSS3BG] for the definitions of the property values.

https://drafts.fxtf.org/css-masking-1/#propdef-mask-border-slice

Name: border-image-slice
Value: [<number [0,∞]> | <percentage [0,∞]>]{1,4} && fill?

https://drafts.csswg.org/css-backgrounds-3/#propdef-border-image-slice

---

The following longhand pairs also have different initial values, different animation types, and numeric CSS types are constrained for one but not the other:

• border-image-slice and mask-border-slice
• border-image-width and mask-border-width
• border-image-outset and mask-border-outset

I am not sure (all) these differences are intentional.

[w3cbot]

svgeesus marked as non substantive for IPR from ash-nazg.

[cdoublev]

Move to w3c/csswg-drafts#13681.